Full opinion text
LIPEZ, Circuit Judge. This complex appeal arises out of the joint criminal prosecution of Emadeddin Muntasser, Muhamed Mubayyid, and Samir Al-Monla for conspiring to defraud the United States by obstructing the functions of the Internal Revenue Service (“IRS”), for corruptly endeavoring to obstruct the due administration of the Internal Revenue laws, for filing false tax returns, for making false statements to agents of the Federal Bureau of Investigation (“FBI”), and for scheming to conceal material facts from a federal agency. The charges stem from each defendant’s involvement with Care International, Inc. (“Care”), a charitable organization incorporated by Muntasser in 1993 with a stated purpose of providing worldwide humanitarian aid. The defendants’ twenty-four day jury trial focused on the circumstances motivating Muntasser’s formation of Care in 1993; the defendants’ failure to disclose some of Care’s activities, such as the publication of certain newsletters from 1993 to 1997; and Care’s support for, and promotion of, Islamic jihad and fighters known as “mujahideen.” The government’s central theory at trial was that Muntasser had established Care in order to fraudulently obtain a tax exemption, so that contributions being used to finance mujahideen overseas could be deducted from individual tax returns as charitable donations. At the close of the government’s case, the district court acquitted Muntasser and Al-Monla of endeavoring to obstruct the administration of the Internal Revenue laws. It found that their tax filings, which formed the basis of the charge, occurred outside of the relevant statute of limitations period. The jury then acquitted AlMonla of making a false statement to an FBI agent, but otherwise convicted the defendants of all counts. Following that verdict, the district court acquitted Muntasser and Al-Monla of having schemed to conceal material facts from a federal agency, and acquitted all three defendants of having conspired to defraud the United States. With respect to the scheme to conceal, it found that the government’s proposed jury instruction, accepted by the court, had narrowed the charge in a way that rendered Muntasser’s and Al-Monla’s acts of concealment immaterial. As to the conspiracy, the court concluded that the government offered insufficient evidence that the defendants had reached the specific agreement described in the indictment. Muntasser, Mubayyid, and the government have appealed. Muntasser argues that the evidence introduced at trial linking Care to organizations financially supporting the mujahideen and jihad, including an alleged predecessor organization that received negative publicity in connection with the 1993 World Trade Center bombing, biased the jury in the appraisal of the government’s evidence on his sole count of conviction, a false statement charge. He also challenges his sentence. Mubayyid appeals from his convictions for filing false tax returns and for endeavoring to obstruct the administration of the Internal Revenue laws, contending that the question that the jury found he answered falsely was fundamentally ambiguous. He also claims that the evidence was insufficient to support his conviction for scheming to conceal material facts. Additionally, with respect to all of his convictions, he claims that he was prejudiced by the introduction of a recorded telephone conversation and joins Muntasser in claiming prejudicial spillover from what the defendants characterize as “terrorism evidence.” The government, for its part, seeks to reinstate the jury’s guilty verdict against all three defendants on the charged conspiracy to defraud the United States. In its view, the district court erred by acquitting the defendants when the government successfully proved a conspiracy that was narrower than, but wholly included within, that alleged in the indictment. After careful consideration, we reverse the district court’s acquittal of the defendants on the conspiracy count, reinstate the jury’s verdict, and affirm the defendants’ other convictions. I. A. Factual Background We recount the essential facts of the case, drawn from the trial record, in the light most favorable to the verdict. E.g., United States v. Poulin, 631 F.3d 17, 18 (1st Cir.2011). Due to the complexity of the issues, we reserve additional factual detail for the analysis that follows. 1. Care’s Formation and Operations Emadeddin Muntasser is a Libyan citizen and a permanent resident alien in the United States. In the early 1990s, Muntasser served as Director of the Boston branch of the Al-Kifah Refugee Center (“Al-Kifah”), the American face of Maktab al-Khidmat (“MAK”), a Pakistan-based organization that openly advocates violent, Islamic jihad and actively supports mujahideen in Afghanistan. In a letter of solicitation introduced at trial, Muntasser described Al-Kifah as “an organization founded by Sh[eikh] Abdullah Azzam to serve the cause of Jihad,” and which “actively supports the Mujahideen in the front.” Among its activities, Al-Kifah’s Boston branch published a pro-jihad newsletter entitled “Al-Hussam,” which translates from Arabic as “The Sword”; it sold books and audiotapes extolling the cause of jihad; and it promoted sermons and lectures by like-minded Muslim leaders. It also solicited substantial charitable donations through the publication of an annual Zakat Calculation Guide. Although the organization advertised itself as a tax-exempt charity, it had never been granted charitable status by the IRS. In early 1993, shortly after the World Trade Center bombing in New York City, both Newsweek and The New York Times ran articles linking the Brooklyn branch of Al-Kifah to “Islamic Militant groups, fighters in Afghanistan, and individuals who were alleged to have committed acts of violence.” Within days, Muntasser dissolved the Boston branch of Al-Kifah and incorporated Care in Massachusetts. According to its articles of incorporation, Care was “organized exclusively for charitable, religious, educational, and scientific purposes including ... human welfare, charitable and relief activities.” The articles listed Muntasser as Care’s President, Munther Baara as Treasurer, and Ahmad Nawras as Secretary, and identified Afif Kadri, Mohamad Akra, and Waseem Abu Yasin as board members. Baara, Nawras, Kadri, Akra, and Yasin had all served in identical positions for the Boston branch of Al-Kifah. The articles also stated, “It is intended that the corporation shall be entitled to exemption from federal income tax under Section 501(c)(3) of the Internal Revenue Code.” Following its incorporation, Care effectively replaced Al-Kifah’s Boston branch. It took over Al-Kifah’s mailbox address and deposited financial contributions into Al-Kifah’s bank account (though these contributions were eventually transferred to an account in Care’s name). Care’s activities also substantially mirrored those of Al-Kifah’s Boston branch, including the sponsoring of pro-jihad speakers, the sale of books and tapes advocating jihad, and the continued publication of the “Al-Hussam” newsletter. Within the organization, individuals referred to Care as “Maktab,” a shorthand reference to MAK. In its own newsletters, Care referred to itself as “the office of services,” a name by which MAK was known in the United States. Like AlKifah, Care also represented itself to the public as “founded by Imam Abdullah Azzam,” even though Abdullah Azzam had died more than three years prior to Care’s formation. At trial, the government presented two experts who testified regarding the overseas operations of MAK, Abdullah Azzam’s philosophy on violent jihad, the general trend of using charitable organizations to covertly finance jihad and mujahideen, and the concept of “economic jihad” — the precept that, “[i]f you cannot be a fighter, fund a fighter.” It also asked a witness to read fifty-five pages of the “AlHussam” newsletters into the record, primarily those sections that demonstrated Care’s commitment to violent jihad and its financial solicitations for the mujahideen. Defendants Al-Monla and Mubayyid had both been associated with Care in some form since 1993, and with Al-Kifah before it. In 1996, Al-Monla replaced Muntasser as President of Care. He served in that capacity until 1998, when he became Treasurer. Mubayyid, who is Al-Monla’s brother-in-law, eventually replaced AlMonla as Care’s Treasurer in 1998 or 1999. He filled that role through at least 2002. 2. Care’s Tax Filings Approximately six weeks after incorporating Care, Muntasser applied to the IRS to have Care designated as a tax-exempt charity. In order to obtain tax-exempt status, an organization must file an initial application for tax exemption, IRS Form 1023, in which the organization demonstrates that it is organized and operated exclusively for a qualifying purpose. In Care’s Form 1023 filing, Muntasser represented that Care had not yet become operational, an inaccurate statement, but that “within a couple months” it would engage in humanitarian projects such as providing “assistance to victims of natural and man-made disasters,” sponsoring “orphans in disaster areas overseas,” and developing “rehabilitation programs for refugees coming from overseas.” Although the form asked for “a detailed narrative description of all of the activities of the organization— past, present, and planned,” Muntasser did not disclose Care’s hosting of religious speakers, its sale of materials advocating jihad, or its publication of the “Al-Hussam” newsletters (by that point, Care had already published at least two “Al-Hussam” newsletters in its own name). Nor did he disclose that Care’s orphan sponsorship program would target the orphans of martyred mujahideen. In response to a question asking for the details of the organization’s fundraising program, Muntasser stated that “mailings” “will commence within the next couple of months.” He did not specifically describe the “Al-Hussam” newsletters or the Zakat Calculation Guide as fundraising devices, nor did he attach them in response to the form’s request for “representative copies of solicitations for financial support.” Lastly, Muntasser denied that Care was an outgrowth of or successor to any other organization, despite Care’s obvious ties to Al-Kifah’s Boston branch. Based on the information provided, the IRS approved Care’s application for tax-exempt status without requesting additional verifying information. At trial, the IRS employee who approved Care’s application testified that he would have requested copies of the “Al-Hussam” newsletter and the Zakat Calculation Guide if their existence had been disclosed in the application. He further testified that, if he had seen the Zakat guide, he would have requested further documentation of Care’s day-to-day activities. Similarly, if Muntasser had disclosed the relationship between Al-Kifah and Care, he would have requested information about Al-Kifah, including whether it was a tax-exempt organization in the United States. In order to maintain its tax exemption, Care had to file annually IRS Form 990, disclosing the earnings and activities of the organization. Between 1993 and 2002, each of the three defendants signed and filed at least one Form 990 on Care’s behalf. In 1996, Muntasser filed delinquent Form 990s for the tax years 1993, 1994, and 1995. In 2000, Al-Monla signed and filed the delinquent 1998 Form 990. In 2000, 2001, and 2002, Mubayyid filed amended Form 990s for the 1997, 1999, and 2000 tax years. None of the Form 990s filed by the three defendants revealed that Care was publishing or had published the “Al-Hussam” newsletters, that Care was operating a website through which it solicited donations and provided access to articles from the “Al-Hussam” newsletters, that Care was regularly hosting pro-jihad speakers, or that Care was selling books and tapes on the subject of jihad. Although Muntasser had failed to disclose these same activities in Care’s initial application, Form 1023, each of the defendants answered “No” when the Form 990s asked whether the organization engaged in any activities that had not previously been reported to the IRS. Instead, each Form 990 filed by the defendants depicted Care as engaging in just four program services: food distribution, cash assistance to orphans and widows, medical assistance to refugees, and grants to other welfare organizations. 3. The Federal Investigation By at least 1999, Care’s activities had drawn the attention of the FBI, which began a formal investigation of both Care and Muntasser. In April of that year, Muntasser was interviewed by the FBI. During that interview, he disclosed that he had traveled to Pakistan in 1994 or 1995. However, he did not volunteer the fact that, during that trip, he had also traveled to Afghanistan and had met with the Afghan warlord Gulbuddin Hekmatyar. He was not asked a question that required such a disclosure. In August of 2001, Mubayyid transferred all of Care’s records out of its offices and into a rented storage unit. Shortly thereafter, Mubayyid was recorded pursuant to a court-approved wiretap conversing with Mohammed Chehade, the executive director of the Global Relief Foundation (“GRF”), about the federal investigation. During the conversation, Chehade implored Mubayyid to remove Care’s records from the storage unit. However, Mubayyid demurred, insisting that he was “afraid that they may think that there is something.... I don’t want to touch anything, so that there is no.” Three days later, the FBI covertly searched the storage unit, pursuant to a court-issued warrant, in order to gather intelligence about the activities of Care and its officers. It catalogued the contents of the unit and copied numerous documents, but it did not remove any materials at that time. In 2003, the FBI executed a search warrant, seizing the contents of the storage locker as well as documents discovered at Mubayyid’s residence. Among the items at the residence was a copy of Care’s Form 1023 filing. Several documents that had been in the storage unit during the 2001 search were not recovered in 2003: the minutes of a 1995 meeting at which officers of Care and of GRF discussed jihad and supporting the “battalion”; a letter signed by Muntasser and Al-Monla pledging support to the Afghan warlord Hekmatyar; and an e-mail sent to Care from a London-based pro-jihad organization that announced an impending war involving “Kosovah-Mujahideen” and requesting aid from Care in the form of money and fighters. Around the time of the seizure, the FBI once again interviewed Muntasser. This time, Muntasser was asked directly whether he had ever traveled to Afghanistan. He repeatedly denied having done so, and he also denied having ever met Hekmatyar. Although an investigating agent testified that he thought Muntasser had been to Afghanistan, he had no information linking him to Hekmatyar. He testified that a truthful response by Muntasser regarding his travel to Afghanistan would have drastically changed the nature of the interview. Later in 2003, Muntasser disclosed his trip to Afghanistan on an Application for Naturalization and admitted the same to an Immigration and Naturalization Service officer in a subsequent interview. B. Procedural History On May 11, 2005, a grand jury returned an indictment charging Muntasser and Mubayyid with one count of scheming to conceal material facts from a federal agency and one count of conspiring to defraud the United States. The indictment also charged Mubayyid with three counts of filing a false tax return for his submission of the Form 990s for the tax years 1997, 1999, and 2000, and it charged Muntasser with one count of making a false statement to a federal agency during his April 2003 FBI interview. On March 8, 2007, a grand jury returned a superseding indictment charging all three defendants with scheming to conceal material facts from a federal agency (Count 1), conspiring to defraud the United States (Count 2), and endeavoring to obstruct the administration of the Internal Revenue laws (Count 8). The 2007 indictment retained the tax return charges against Mubayyid (Counts 3-5) and the false statement charge against Muntasser (Count 6). Additionally, it charged AlMonla with one count of making a false statement to a federal agency (Count 7) for allegedly lying to the FBI when he denied knowing a man by the name of Bassam Kanj. Following the government’s presentation of evidence at trial, the defendants moved for a judgment of acquittal on Counts 1, 2, and 8, arguing that the evidence at trial was insufficient to prove the charged crimes, and also that the relevant statutes of limitation precluded convictions on Counts 1 and 8. See Fed.R.Crim.P. 29. The trial judge acquitted Muntasser and AlMonla on Count 8, obstructing the Internal Revenue laws, because those defendants’ tax filings on behalf of Care, Forms 1023 and 990, were outside the statute of limitations, and their more recent statements to the FBI, even if proven false, could not have been material to the IRS. It otherwise denied the motions. With respect to the Count 2 conspiracy charge, however, the judge expressed significant reservations about the sufficiency of the evidence. The defendants called just one witness— a tax expert' — before the case was submitted to the jury. The jury acquitted AlMonla on Count 7, the false statement count, and returned a guilty verdict on all other charges. In response to the defendants’ renewed Rule 29 motion, the district court set aside the jury’s verdict against all three defendants on Count 2 and against Muntasser and Al-Monla on Count 1. According to the district court, Count 2 charged a conspiracy with a single, unitary object — obtaining Care’s tax-exempt status in 1993 and maintaining it thereafter — but the government had presented insufficient evidence that Muntasser conspired with anyone prior to obtaining Care’s tax-exempt status in 1993. The district court’s ruling on Count 1, which charged them with scheming to conceal material facts from a federal agency, was a function of the government’s proposed jury instruction restricting the federal agency affected to the IRS alone. As with Count 8, the district court again concluded that the only conduct by Muntasser and Al-Monla that would be material to the IRS was time-barred. The district court’s combined rulings left Al-Monla acquitted of all charges, and Muntasser convicted only of his 2003 false statement to the FBI (Count 6). Mubayyid, however, was convicted of five counts: one count of scheming to conceal material facts from the IRS (Count 1), one count of endeavoring to obstruct the administration of the Internal Revenue laws (Count 8), and three counts of filing a false tax return (Counts 3-5). Muntasser received a twelve-month sentence of incarceration, twice that recommended by the United States Sentencing Guidelines for a false statement conviction. Mubayyid was sentenced to eleven months’ incarceration and thirty-six months of supervised release. II. This appeal involves the following claims: The government appeals from the district court’s post-verdict acquittal of all three defendants on the conspiracy charged in Count 2. It claims that the district court erred by finding evidentiary insufficiency in a variance in proof that did not prejudice the defendants. It does not appeal the district court’s acquittal of Muntasser and Al-Monla for scheming to conceal material facts from the IRS, and for obstructing the due administration of the IRS. Mubayyid argues that his convictions for filing false tax returns are legally unsupportable because they rest on his answer to a fundamentally ambiguous question. He also claims that the government’s evidence was insufficient with respect to the charged scheme to conceal, and that both the erroneous admission of certain evidence and a statement by the prosecutor in closing arguments prejudiced his trial. Muntasser contends that the admission of inflammatory terrorism evidence, relevant only to the conspiracy and the tax-related counts of which he was acquitted, spilled over into the jury’s consideration of his false statement charge. He also contends that his twelve-month sentence is unreasonable. We address the parties’ claims seriatim. A. The Government’s Claim We begin by addressing the government’s appeal because the correctness vel non of the district court’s post-verdict acquittal informs our analysis of several of the defendants’ claims of error. Our review is de novo, and we may uphold the judgment of acquittal only if the evidence, viewed in the light most favorable to the government, could not have persuaded any trier of fact of the defendants’ guilt beyond a reasonable doubt. E.g., United States v. Merlino, 592 F.3d 22, 29 (1st Cir.2010). “So long as ‘the guilty verdict finds support in a plausible rendition of the record,’ it must be allowed to stand (and the acquittal must be reversed).” United States v. Rivera Rangel, 396 F.3d 476, 482 (1st Cir.2005) (quoting United States v. Rivera-Ruiz, 244 F.3d 263, 266 (1st Cir.2001)). Count 2 of the indictment charged the defendants with conspiring to defraud the United States by obstructing the functions of the IRS, in violation of 18 U.S.C. § 371. See generally United States v. Klein, 247 F.2d 908 (2d Cir.1957). Specifically, the indictment alleged that the purpose of the conspiracy was as follows: impeding, impairing, interfering, obstructing and defeating through deceit, craft, trickery, and dishonest means the lawful functions of the [IRS] in the ascertainment, assessment, and determination of whether [Care] qualified and should be designated as a 501(c)(3) organization in 1993 and should continue to be accorded status as [a] 501(c)(3) organization thereafter. The district court acquitted the defendants on Count 2 based on its finding that the above language of the indictment described a conspiracy with a “specific purpose: impairing the IRS’s determination as to whether Care qualified for, and should continue to be accorded, charitable status.” The district court acknowledged that, where a single conspiracy embraces multiple unlawful objects, a jury may convict upon proof that the defendants agreed to any one of those objectives. See Griffin v. United States, 502 U.S. 46, 57, 112 S.Ct. 466, 116 L.Ed.2d 371 (1991). It held, however, that “this was not a multiple-object conspiracy,” but rather a conspiracy with “a single, unitary object.” Because the evidence at trial was insufficient to prove that anyone agreed with Muntasser to obstruct the IRS prior to Care’s initial application for tax-exempt status in 1993, the district court reasoned that the government had failed to prove the specific conspiracy charged: Again, the government charged a single agreement, an agreement to obtain and maintain tax-exempt status for Care. There was no evidence that there was a conspiracy to obtain that status, and no evidence that there was a conspiracy of any kind in or about 1993. Even if Mubayyid or Al-Monla, or both, agreed with Muntasser in 1995 or later to maintain the charitable status of Care or to commit another offense, that is not the agreement charged in the indictment. To sustain a conviction there must be sufficient evidence of the conspiracy charged in the indictment — ■ that conspiracy and not some other conspiracy. On appeal, the government concedes that it presented insufficient evidence at trial to prove that any of the defendants conspired to obtain Care’s tax exemption in 1993. It also fails to pursue its argument, made in the district court, that Count 2 of the indictment alleged a conspiracy with multiple objects. Nevertheless, the government urges us to reinstate the jury’s verdict, casting the issue as one of evidentiary variance, rather than insufficiency. A variance occurs when the facts proved at trial differ materially from those alleged in the indictment without altering the crime charged. United States v. Tormos-Vega, 959 F.2d 1103, 1115 (1st Cir.1992). Traditionally, a claim of variance is raised on appeal by a defendant seeking to overturn a judgment of conviction. In those situations, we have said that a variance is not a ground for acquittal, provided that the facts actually proven at trial are sufficient to convict the defendant of the charged crime and the variance did not prejudice the defendant. See United States v. Glenn, 828 F.2d 855, 858 (1st Cir.1987) (Breyer, J.). The government claims that it succeeded in proving a narrower conspiracy prohibited by the same statutory provision charged, 18 U.S.C. § 371, and comprised wholly of acts clearly set forth in the indictment, amounting to no more than a non-prejudicial variance. The defendants offer three rejoinders. First, they claim that a variance is only permissible where the indictment is narrowed in a way that does not alter an “essential element” of the charged offense. Alterations to the object of a unitary conspiracy, they contend, fundamentally change the crime of conviction from that charged. Second, they claim that, even if the variance was otherwise permissible, it was prejudicial to their defense, requiring that we affirm the district court’s acquittal. Third, they claim that, in any event, the government failed to produce sufficient evidence of a naiTower conspiracy among the defendants. 1. Did the Variance Alter the Crime Charged? In general, a defendant can hardly be heard to complain when the govern-merit’s proof at trial establishes “a scheme similar to but somewhat narrower in breadth and malignity than that charged in the indictment.” United States v. Mueffelman, 470 F.3d 33, 38 (1st Cir.2006). The defendants argue, however, that the object of a conspiracy is an “essential element” of the crime charged, see United States v. Roshko, 969 F.2d 1, 5 (2d Cir.1992), and that permitting a variance as to that object is improper. They suggest that the government’s failure to establish the precise object of the conspiracy charged is substantively different from the cases in which we have permitted a variance — typically where the government has failed to establish a particular manner or means, or that the crimes occurred in the particular time frame alleged. As the defendants put it, “An agreement to maintain a tax-exempt status may encompass a narrower range of activity than a conspiracy to obtain and maintain tax-exempt status, but it is also a different agreement.” The defendants’ claim implicates a number of often-overlapping limitations on the government’s power to prosecute its citizens. As far as is relevant to the government’s appeal, these limitations are encapsulated by the distinction in our law between mere variance and the constructive amendment of an indictment. See United States v. Brandao, 539 F.3d 44, 57 (1st Cir.2008) (“The prohibition on constructive amendment exists to preserve the defendant’s Fifth Amendment right to indictment by grand jury, to prevent re-prosecution for the same offense in violation of the Sixth Amendment, and to protect the defendant’s Sixth Amendment right to be informed of the charges against him.”). In contrast to a variance, a constructive amendment occurs where the crime charged has been altered, “either literally or in effect,” after the grand jury last passed upon it. E.g., United States v. Bunchan, 626 F.3d 29, 32 (1st Cir.2010) (quoting United States v. Celestin, 612 F.3d 14, 24 (1st Cir.2010)). “The concepts of constructive amendment and variance are closer to a continuum than exclusive categories.” Mueffelman, 470 F.3d at 38. “Save at either end of the spectrum,” it is not always clear what distinguishes a permissible variance from an impermissible constructive amendment. Haines v. Risley, 412 F.3d 285, 291 (1st Cir.2005); see also United States v. Adamson, 291 F.3d 606, 615 (9th Cir.2002) (“The line between a constructive amendment and a variance is at times difficult to draw.”); 3 Charles Alan Wright & Sarah N. Welling, Federal Practice and Procedure, Criminal § 516 (4th ed.2011) (“The distinction between variances and constructive amendments is a matter of degree, and the distinction is rather shadowy.” (footnote omitted)). The Supreme Court has interpreted the Fifth Amendment’s Presentment Clause to mean that, “after an indictment has been returned[,] its charges may not be broadened through amendment except by the grand jury itself.” Stirone v. United States, 361 U.S. 212, 215-16, 80 S.Ct. 270, 4 L.Ed.2d 252 (1960); see also id. at 217-19, 80 S.Ct. 270 (holding that an indictment was unconstitutionally broadened where prosecution offered evidence of two theories of liability, but the grand jury indicted defendant only on the first theory). It has also expressly rejected the proposition that “a narrowing of the indictment constitutes an amendment that renders the indictment void.” United States v. Miller, 471 U.S. 130, 144, 105 S.Ct. 1811, 85 L.Ed.2d 99 (1985). The Miller Court held that the Fifth Amendment was not violated where the government’s variance “added nothing new to the grand jury’s indictment and constituted no broadening,” id. at 145, 105 S.Ct. 1811, but rather proved “a significantly narrower and more limited, though included, fraudulent scheme,” id. at 131, 105 S.Ct. 1811. We have since embraced, as a “well-established” principle, that a court may “narrow the indictment’s charges without adding any new offenses.” Celestin, 612 F.3d at 25 (alteration omitted) (quoting Miller, 471 U.S. at 138, 105 S.Ct. 1811) (internal quotation marks omitted). The defendants seek to distinguish Miller on the ground that “what was removed from the case was in no way essential to the offense on which the jury convicted.” See Miller, 471 U.S. at 145, 105 S.Ct. 1811. They rely on a Second Circuit case, United States v. Roshko, for the proposition that, “[wjithout question, the object of a conspiracy constitutes an essential element of the conspiracy offense.” 969 F.2d at 5. Thus, they claim, “a variance may be permissible where it alters the means of a charged conspiracy — not where it alters the object.” To the extent that the defendants argue that the object of a conspiracy is always an improper subject for a variance, they are wrong. In United States v. Glenn, this circuit’s pathmarking precedent articulating the variance analysis, we upheld a defendant’s conviction for a narrower conspiracy than the one charged. There, the indictment charged two defendants with a single, overarching conspiracy to import both marijuana and hashish. Glenn, 828 F.2d at 857. The government’s proof at trial, however, evidenced two separate conspiracies, each with a narrower, distinct object of importing only a single drug. Id. Explaining that “conspiracy law, like most criminal law, focuses on the activities of an individual defendant,” id., the Glenn court set out to determine “what kind of agreement or understanding existed as to each defendant,” id. (emphasis omitted) (quoting United States v. Borelli, 336 F.2d 376, 384 (2d Cir.1964)) (internal quotation mark omitted). Although it concluded that the evidence was insufficient to convict the defendants “of the conspiracy that the indictment charged, namely, the conspiracy to import and possess both marijuana from Thailand and hashish from Pakistan,” it concluded that a permissible variance had occurred because the evidence remained sufficient to permit a jury, under a proper set of instructions, to convict one defendant of a “related, similar conspiracy” to import just one of the drugs. Id. at 858-61. Roshko is not to the contrary. It involved a conspiracy to defraud the United States whose object was expressly defined as “seeking changes in the immigration status of an alien based on a sham marriage to a United States citizen that was falsely represented to be genuine.” Roshko, 969 F.2d at 2. At trial, the government introduced evidence that the defendant had conspired in the marriage of her future husband, an immigrant from Israel, to a United States citizen, in order to secure his green card. Id. at 3. It further offered evidence of that couple’s subsequent divorce and of the defendant’s marriage to her now-permanent-resident-alien husband (which ultimately resulted in her successful application for a green card). Id. When the defendant raised a statute of limitations challenge to the evidence of her husband’s sham marriage, the government argued that the conspiracy broadly embraced both marriages, and that the prosecution was therefore timely. Id. at 4. The Second Circuit, emphasizing that the indictment specifically charged a purpose to change the status of “an alien” through marriage to “a United States citizen,” found that the indictment was not so broad as the government claimed. Id. at 5-6 (emphasis added). It held that the unlimited introduction of evidence related to the second marriage, combined with the government’s arguments that such conduct was part and parcel of the conspiracy, was impermissible because it “could easily have created a basis for conviction which the grand jury did not intend to create.” Id. at 6. Roshko thus stands for the unobjectionable proposition that the government’s broadening of an indictment’s charges through proof at trial constructively amends an indictment. To the extent that the defendants instead argue that the object of the conspiracy here, because of the way in which it was charged, may not be narrowed without fundamentally changing the offense, their claim is unpersuasive. “[T]he line between ‘the crime charged’ and ‘the facts charged’ is inherently fuzzy.” Mueffelman, 470 F.3d at 38. Hence, our practice has been to look to statutory elements in response to claims by defendants that “the crime charged” has been changed. We have said that, “[s]o long as the statutory violation remains the same, the jury can convict even if the facts found are somewhat different than those charged.” United States v. Twitty, 72 F.3d 228, 230 (1st Cir.1995); cf. Glenn, 828 F.2d at 858 (noting that one question in variance analysis is whether sufficient evidence exists of “related, similar conspiracy” to one charged). Here, the titular crime was not altered. The defendants were indicted under 18 U.S.C. § 371, which criminalizes conspiracies with an object “to defraud the United States, or any agency thereof in any manner or for any purpose.” Cf. Mueffelman, 470 F.3d at 38 (finding no constructive amendment where “Mueffelman was charged with mail fraud and convicted of mail fraud”). Pursuant to that provision, the government was required to prove three elements: “an agreement, the unlawful objective of the agreement, and an overt act in furtherance of the agreement.” United States v. Barker Steel Co., 985 F.2d 1123, 1127-28 (1st Cir.1993) (quoting United States v. Hurley, 957 F.2d 1, 4 (1st Cir.1992)). “The objective of the agreement is unlawful if it is ‘for the purpose of impairing, obstructing or defeating the lawful function of any department of Government.’ ” Id. at 1128 (quoting Dennis v. United States, 384 U.S. 855, 861, 86 S.Ct. 1840, 16 L.Ed.2d 973 (1966)). These elements were fully satisfied by so much of the indictment as charged the defendants with conspiring “to defraud the United States for the purpose of impeding, impairing, interfering, obstructing and defeating through deceit, craft, trickery, and dishonest means the lawful functions of the [IRS].” That language is also consonant with the narrower conspiracy proven. To be sure, the government’s indictment did not stop there. It specifically alleged that the agreed-upon purpose of the defendants’ fraud was to obstruct the IRS “in the ascertainment, assessment, and determination of whether Care International, Inc., qualified and should be designated as a 501(c)(3) organization in 1993 and should continue to be accorded status as [a] 501(c)(3) organization thereafter.” As the district court noted, this language appears in the key charging paragraph, is identified as a component of the conspiracy’s “purpose,” and appears prior to and apart from the five paragraphs of the indictment setting forth the “manner and means by which the conspiracy was sought to be accomplished” and the nine paragraphs identifying the overt acts committed in furtherance of the conspiracy. The question is whether, and to what extent, this additional charging language precluded the government from proving a narrower conspiracy that embraced only the agreement of the defendants to act unlawfully to maintain Care’s tax-exempt status. We have found no indications in our case law that, as an element of the offense, the unlawful object of a § 371 conspiracy must be defined with the level of specificity to which the defendant now seeks to hold the government. To the contrary, we have previously declined to parse the conspiratorial object so finely. See United States v. Goldberg, 105 F.3d 770, 774 (1st Cir.1997) (“[W]e see no sharp distinction under section 371 between a purpose to file [false tax] documents and a purpose to interfere [with the functions of the IRS].”); cf. Dennis, 384 U.S. at 863, 86 S.Ct. 1840 (rejecting claim that defendants’ specific purpose of filing false documents in violation of another statute precluded trial under general charge of conspiracy to defraud, noting that indictment under the broader charge is permissible so long as it “properly reflects the essence of the alleged offense”). We have also held, in other contexts, that where the government’s charging language identified an element of the crime with greater specificity than was required by the statute, the alteration of that additional language had “no bearing on the substance of the charge.” United States v. Dowdell, 595 F.3d 50, 68 (1st Cir.2010) (finding no constructive amendment in government’s clarification of drug type identified in indictment where charged crime “prohibits distribution of any controlled substance regardless of type,” and thus “the government could technically have omitted reference to a particular controlled substance altogether”). This approach is consistent with the approach taken in other circuits. See, e.g., United States v. Kuenstler, 325 F.3d 1015, 1022 (8th Cir.2003) (treating as surplusage language in the indictment that described the object of the conspiracy in detail exceeding that which was needed to make out the statutory offense); United States v. Garcia-Paz, 282 F.3d 1212, 1215-17 (9th Cir.2002) (holding that language preceded by the phrase “to wit” in the indictment is mere surplusage that may be disregarded and need not be proven); United States v. Pumphrey, 831 F.2d 307, 309 (D.C.Cir.1987) (“[E]xcess allegations in an indictment that do not change the basic nature of the offense charged need not be proven and should be treated as mere surplus-age.”). Thus, what is striking about the language relied upon by the defendants for the unitary conspiracy theory is that it is needless in the purpose portion of the indictment. If the indictment’s reference to “the ascertainment, assessment, and determination of whether [Care] qualified and should be designated as a 501(c)(3) organization in 1993 and should continue to be accorded status as [a] 501(c)(3) organization thereafter” had appeared in the section of the indictment describing the conspiracy’s “manner and means,” rather than its “purpose,” the defendants would have no argument at all. Hence, the defendants’ argument challenging the government’s right to prove a narrower conspiracy elevates form over substance. All of the material in the “manner and means” portion of the indictment, along with the overt acts alleged, is the specification of the ways in which the defendants sought to accomplish the conspiracy. Given the sufficiency of the more broadly stated purpose of the conspiracy and the detailed specification of conduct in its “manner and means” portion, the language at issue could have been omitted altogether without affecting the sufficiency of the indictment. See United States v. Troy, 618 F.3d 27, 34 (1st Cir.2010) (“[T]he statutory language may be used in the indictment to describe the offense, ‘but it must be accompanied with such a statement of the facts and circumstances as will inform the accused of the specific offence, coming under the general description, with which he is charged.’ ” (quoting Hamling v. United States, 418 U.S. 87, 117-18, 94 S.Ct. 2887, 41 L.Ed.2d 590 (1974))). In light of the foregoing considerations, the government has demonstrated that variance, rather than constructive amendment, is the proper lens through which to view the narrowing of the conspiracy that occurred in this case. The allegations in the indictment charging, in the words of the district court, a conspiracy with a “single, unitary object” are not indispensable or “essential” to the integrity of that document. Indeed, they were effectively surplusage. The government is not seeking to reinstate the defendants’ conviction on the basis of a crime other than the one with which they were charged. Although we hold the government to its charging decisions, we must also hold defendants to so much of their criminal conduct that the government has properly charged and successfully proven. 2. Was the Variance Prejudicial? As noted, to be grounds for reversal, a variance must be severe enough to affect the defendant’s substantial rights. Tormos-Vega, 959 F.2d at 1115 (citing Berger v. United States, 295 U.S. 78, 82, 55 S.Ct. 629, 79 L.Ed. 1314 (1935)). “The ‘substantial rights’ protected by this rule are that the defendant have sufficient knowledge of the charge against him in order to prepare an effective defense and avoid surprise at trial, and to prevent a second prosecution for the same offense.” Id. In addition, a variance can affect a defendant’s substantial rights where, in cases with multiple defendants, proof that one defendant was involved in one conspiracy leads the jury to believe that another defendant was involved in a separate conspiracy. Id. We review de novo whether a variance affected a defendant’s substantial rights. United States v. Fornia-Castillo, 408 F.3d 52, 67 (1st Cir.2005). The defendants claim that they tailored their defense strategy at trial to their expectation that the government was obligated to prove the entire conspiracy as charged. Thus stated, the defendants’ claim of prejudice is not one about fair notice of the charges or conduct at issue. Instead, their claim of prejudice rests uneasily on their misunderstanding about the legal sufficiency of the government’s narrower proof. To the extent that the defendants believed that the government’s conspiracy charge would fail because the government could only prove the narrower conspiracy to maintain Care’s tax-exempt status, they misunderstood the law of conspiracy in this circuit. That misunderstanding cannot support a claim of prejudice. We have previously rejected similar claims in analogous circumstances. See Mueffelman, 470 F.3d at 38-39 (rejecting a claim of prejudice where the defendant structured his defense to combat a claim that the government was not required to prove); accord United States v. Davis, 679 F.2d 845, 852 (11th Cir.1982) (“Appellants’ contention that they suffered prejudice because they were prepared to defend against the larger conspiracy but not the smaller one is nothing more than an argument that they had less of a defense against the smaller conspiracy since the larger one may not have existed.”). Moreover, even if the nature of the prejudice claimed by the defendants was legally relevant (which it is not), the defendants have not pointed to any evidence in the voluminous trial record that reflects a less-than-vigorous defense. Although the defendants do not elaborate in their briefs on their prejudice claim, counsel for the defendants asserted at oral argument that, because they believed the government’s inability to prove a conspiracy to obtain Care’s tax-exempt status in 1993 would be fatal to the conspiracy charged, their defense did not emphasize the weaknesses of the government’s circumstantial evidence of any narrower agreement to maintain that status. Our own review of the record does not support the defendants’ claim. To begin with, although the government has conceded on appeal that it charged a unitary conspiracy to both obtain and maintain Care’s tax exemption, it argued below that the indictment charged a multiple-object conspiracy. The trial judge did not reject that argument until after the close of the government’s evidence. In their initial Rule 29 motion, the defendants challenged Count 2 only on the ground that the government had failed to demonstrate that the defendants had, in fact, reached an agreement among themselves sometime after 1993. It was not until their memorandum in support of a renewed Rule 29 motion that the defendants first suggested that the indictment did not charge a conspiracy with separate objects. Similarly, the defendants’ proposed jury instruction on the conspiracy count merely specified that the jury must be required to find “that the object of their agreement was to impede or thwart the IRS as alleged in the indictment.... If you find that tax fraud was not the object of the conspiracy, then even if you find that tax fraud was a foreseeable consequence of the conspiracy, you must find the defendants not guilty.” Again, the defendants’ own conduct reveals no particular emphasis on the unity of the charged object. Nor have we found that the defendants placed an undue emphasis on defending against the government’s proof of Muntasser’s agreement with unindicted co-eonspirators in 1993. In fact, Muntasser’s principal defense to the Count 2 conspiracy was that he withdrew from the conspiracy by 1996. He expressed this position through the opening statement of his defense counsel, through cross-examination of witnesses, including Afif Kadri, one of Care’s founding officers, and again through closing argument. The absence of outward indications of prejudice is not a surprise: a less-than-vigorous defense of the conduct underlying the narrower conspiracy would have compromised the defendants’ defense of other charges. For example, the evidence supporting the narrower conspiracy was directly relevant to Count 1, which charged all three defendants with a scheme to conceal material facts from the FBI, IRS, and INS, and Count 8, which charged all three defendants with endeavoring to obstruct the due administration of the Internal Revenue laws. Thus, even if the defendants subjectively believed that the government’s failure to prove a conspiracy to fraudulently obtain Care’s tax exemption in 1993 was fatal to the conspiracy claim, the defendants had strong incentives to continue to challenge the evidence that most demonstrated their willing agreement to fraudulently maintain that exemption in subsequent years. Finally, in a different version of their prejudice argument, the defendants claim that the variance affected their substantial rights because, by charging a larger conspiracy than it could ultimately prove, the government was permitted to introduce much of the so-called “terrorism” evidence, relevant to Muntasser’s initial motivation for incorporating Care, which would not have been admissible if the government had charged only the narrower conspiracy at the outset. According to the defendants, “The government should not be permitted to have it both ways” (i.e., securing the admission of potentially inflammatory evidence through a broadly worded charge while securing a conviction on a narrower ground). The defendants have underestimated the extent to which the challenged evidence was relevant to the narrower conspiracy. The most inflammatory evidence presented at trial was the content of Care’s “AlHussam” newsletters, with its accounts of the violent jihad being conducted overseas, described by the district court as “blood curdling.” While the newsletters were probative of whether Care was a successor to Al-Kifah and whether Muntasser incorporated Care to legitimize the tax exemption Al-Kifah incorrectly claimed, they also played a central role in explaining why Care’s Form 990 filings were fraudulent. Similarly, the expert testimony explaining the concept of economic jihad, and thus the way in which Care’s “orphan sponsorship program,” among other things, promoted and supported the mujahideen and jihad, would have been independently admissible to prove the pattern of conscious concealment that reflected agreement among the defendants when they filed the Form 990s. Consequently, in this way as well, the variance in proof at trial did not prejudice the defendants’ substantial rights. 3. Did the Government Prove the Narrower Conspiracy? The defendants contend that the government may not rely on a variance to reinstate their conspiracy conviction because the evidence at trial was insufficient to demonstrate a narrower conspiracy among the defendants. As noted, the general conspiracy statute, 18 U.S.C. § 371, criminalizes the conspiring of two or more people “to commit any offense against the United States, or to defraud the United States, or any agency thereof in any manner or for any purpose.” The defendants were charged under § 371’s defraud clause with conspiring to defeat the IRS’s proper assessment and collection of tax revenue, commonly known as a Klein conspiracy. See Goldberg, 105 F.3d at 773. To prove a Klein conspiracy, the government is required to establish both “an agreement whose purpose was to impede the IRS (the conspiracy),” and the knowing participation of each defendant in that conspiracy. United States v. Adkinson, 158 F.3d 1147, 1154 (11th Cir.1998). Although “[v]olumes could be written” on the “subtle problems in discriminating ‘purpose’ from ‘knowledge’ and in separating the objects of a conspiracy from its more remote consequences,” it is well settled in this circuit that, “where the conspirators have effectively agreed to falsify IRS documents to misstate or misattribute income, ... the factfinder may infer a purpose to defraud the government by interfering with IRS functions.” Goldberg, 105 F.3d at 774. We therefore turn our attention to the evidence at trial that indicates the defendants’ knowing agreement to falsify Care’s tax filings. The government presented no direct evidence of an agreement either among the defendants or between any defendant and an unindicted co-conspirator. Of course, this is unsurprising. By their very nature, criminal conspiracies are clandestine and inchoate, and “may be completed in the brief period needed for the formation of the agreement and the commission of a single overt act in furtherance of the conspiracy.” Boyle v. United States, 556 U.S. 938, 129 S.Ct. 2237, 2246, 173 L.Ed.2d 1265 (2009); see also United States v. Rodriguez-Velez, 597 F.3d 32, 39 (1st Cir.2010). Accordingly, the government is not required to offer proof of an express agreement. Rather, it is a “well-established legal principle that a conspiracy may be based on a tacit agreement shown from an implicit working relationship.” United States v. Patrick, 248 F.3d 11, 20 (1st Cir.2001). As we detail below, there was sufficient evidence here of a deliberate, coordinated effort among the defendants reflecting just such a tacit agreement. The government’s theory at trial was that the defendants, through a series of fraudulent Form 990 filings, intentionally concealed from the IRS the fact that Care’s activities substantially advanced two non-charitable purposes: financial support of the mujahideen and promotion of jihad. During their tenure with Care, each defendant filed at least one Form 990. Muntasser signed and filed Care’s Form 990s for the 1993, 1994, and 1995 tax years. He did so with considerable assistance from Waseem Yassin, an unindicted co-conspirator and an officer of both Care and Al-Kifah. For example, Yassin contacted an attorney to assist in the preparation of the forms, he provided the attorney with Muntasser’s materially false Form 1023 application for tax exemption, and he gave an incomplete description of Care’s activities to the attorney when that information was requested. Al-Monla had been involved with Care since 1993, became more involved in 1995, and eventually succeeded Muntasser as Care’s President in 1996. The government introduced evidence that showed how, prior to becoming President, Muntasser and Al-Monla worked closely together to advance Care’s non-charitable purposes. For example, the evidence showed that the two defendants jointly met with Mohammed Chehade, the executive director of GRF, to discuss the solicitation of donations and “coordinating with the battalion.” It also introduced a written pledge of support to the Afghan warlord Gulbuddin Hekmatyar, which was signed by Muntasser, Al-Monla, Yassin, and another unindicted co-conspirator. In 1996, the year Muntasser became president, Yassin stated in a recorded conversation that his involvement in Care was waning and that he would be handing the reigns over to someone else. Yassin subsequently provided Al-Monla with Care’s financial information. Following his tenure as President, Al-Monla served as Care’s Treasurer in 1998. He signed and filed Care’s Form 990 for that year. Mubayyid, Al-Monla’s brother-in-law, performed volunteer work for Care in 1993 and 1994 before leaving the country for several years. In 1998 or 1999, Mubayyid succeeded Al-Monla as Care’s Treasurer. He signed and filed amended Form 990 returns for the 1997, 1999, and 2000 tax years. The Form 990s filed by the defendants were nearly identical, regardless of the preparer. Substantially mirroring the Form 1023 submitted by Muntasser in 1993, each return listed only the same four program accomplishments: food distribution, cash assistance to orphans and widows, medical assistance for refugees, and grants to other welfare organizations. As we explain below, however, the evidence showed that Care’s day-to-day activities and objectives were markedly different than those reported to the IRS. The consistency of the misrepresentations over a span of nearly ten years and the failure of the defendants to disclose precisely those activities that were most likely to jeopardize Care’s tax-exempt status provide strong circumstantial evidence that the defendants were operating under an implicit agreement. See, e.g., United States v. Shea, 211 F.3d 658, 665 (1st Cir.2000) (pointing to evidence of “a common and continuing aim, similar methods of operation, continuity in personnel, and interdependence” to prove conspiracy); cf. United States v. Niemi, 579 F.3d 123, 127 (1st Cir.2009) (“[Ijnterdependence may be shown where one participant knows that his own success depends on the continued existence and health of the [unlawful] organization as a whole.”). That the misrepresentations came from defendants who had assumed substantial leadership roles in the organization; who, in those roles, had primary authority over Care’s tax filings, which were central to the fraud; and who succeeded one another in those roles, further negate the alternative possibility that any falsity was the product of separate, individual misunderstandings about the required disclosures. Cf. United States v. Peters, 732 F.2d 1004, 1007 (1st Cir.1984) (“The jury could reasonably have disbelieved that [defendants], as cousins and as president and vice president, respectively, of a relatively small company, acted entirely independently of one another ____” (footnote omitted)). While the above evidence demonstrates an implicit agreement among the defendants, other evidence shows that the defendants had knowledge that their Form 990 submissions were materially false. To begin with, the evidence showed that Care was a small, tight-knit organization whose members were actively and intimately involved in its cause. Its officers were volunteers whose roles were not rigidly segregated. We have previously held that an organization’s small size and informal structure may support a jury’s inference that the organization’s officers had knowledge of and voluntarily participated in a conspiracy. See United States v. Pesaturo, 476 F.3d 60, 72 (1st Cir.2007). Additionally, the evidence at trial indicated that financial support of the mujahideen and promotion of jihad were Care’s primary purposes. The “Al-Hussam” newsletters were replete with exhortations to join the jihad or to finance the mujahideen. The Zakat Calculation Guide distributed by Care described it as “imperative” to “give part of your Zakat to Mujahideen” (which it defined as “those who are going out for Jihad, fighting in the path of Allah”) because “the Mujahideen represent the most needy category today since they are facing a shortage of financial support.” Care’s website similarly contained overt solicitations for support of the mujahideen. Witnesses testified that, in addition to distributing the “AlHussam” and the Zakat guide, Care was selling books and tapes advocating jihad at the lectures of religious speakers that it hosted. Indeed, the government even introduced a recorded phone conversation between Al-Monla and the head of another Islamic charity, in which Al-Monla described Care as existing on “the rear lines” and “financing the brothers picking apples,” a reference to Care’s financial support of the mujahideen. Through its solicitations, Care collected nearly two million dollars in untaxed donations. Many of the donation checks received by Care during this time expressly indicated that the funds were to be used for “mujahideen,” “fighters,” “martyrs,” and “Jihad.” Some checks specified particular countries, or even particular groups of fighters, for which the funds should be used. For example, three checks presented to the jury bore the memo lines: “Bosnia mujahideen,” “Jihad Bosnia,” and “mujahideen Bosnia, 9th Battalion.” During this time, Care deposited checks made out to Al-Kifah and even to “Human Services Office,” referring to MAK. The government introduced evidence of personal checks from each of the defendants to Al-Kifah or Care containing similar instructions. Muntasser made a donation to Al-Kifah shortly after Care’s formation in April 1993 in which he indicated that the funds were “Zakat for the mujahideen in Afghanistan ... Zone 1.” He subsequently made a donation to Care in which he stated that his donation was for “renewing the sponsorship of the family of a martyr.” Despite not being a formal officer at the time, Mubayyid made two donations to Care in 1993 for “Printing of the Al-Hussam” and “Al-Hussam and pilgrimage.” A check from Al-Monla in 1993 simply reads, “Buying Bosnia.” This evidence makes plain the defendants’ intimate knowledge of the very activities and purposes of Care that were concealed through the submission of incomplete and inaccurate Form 990s. We are of course always wary of the dangers associated with a § 371 conspiracy. See Goldberg, 105 F.3d at 775 (“[T]he defraud clause of section 371 has a special capacity for abuse because of the vagueness of the concept of interfering with a proper government function.”). Its broad sweep can capture the innocent as well as the culpable. Cf. Dennis, 384 U.S. at 860, 86 S.Ct. 1840. This is not such a case. The defendants, well known to each other, succeeded each other as authority figures in a small organization that benefitted from the perpetuation of a fraudulent tax status. Given the significance of the factual misrepresentations when juxtaposed with the single-mindedness of Care’s apparent mission, given the overlap among the defendants and the closeness of their working relationships, and given the consistency of the misrepresentations necessary to sustain the fraud for so long, the government’s evidence sufficed to prove a narrower conspiracy to fraudulently maint