Full opinion text
OPINION IKUTA, Circuit Judge: Jesse James Andrews appeals from the district court’s denial of all but one of the claims raised in his petition for a writ of habeas corpus under 28 U.S.C. § 2254. The state cross-appeals the district court’s grant of relief on Andrews’s claim that his counsel’s assistance was ineffective at the penalty phase of his capital murder trial. We dismiss as unripe the claim the district court certified for appeal, and deny Andrews’s motion to expand the certificate of appealability to include uncertified claims. We reverse its grant of relief on the ineffective assistance claim because, under 28 U.S.C. § 2254(d)(1), the California Supreme Court did not unreasonably apply Supreme Court precedent in concluding that Andrews was not prejudiced by any deficient performance by his counsel. I A On December 9, 1979, police were called to a Los Angeles apartment, where they found the bodies of three murder victims. People v. Andrews, 49 Cal.3d 200, 260 Cal.Rptr. 583, 776 P.2d 285, 288 (1989). The murder victims were Preston Wheeler, who lived in the apartment, Patrice Brandon, and Ronald Chism. Id. The California Supreme Court described the murder scene as follows: Wheeler had been stabbed in the chest six times and shot in the neck at close range with either a .32- or .357 — caliber weapon. His face and head were bruised, and his face had been slashed with a knife. Brandon and Chism had been strangled with wire coat hangers. Their faces were bruised, Chism’s extensively. Brandon’s anus was extremely dilated, bruised, reddened and torn, consistent with the insertion of a penis shortly before her death. There was also redness around the opening of her vagina, and vaginal samples revealed the presence of semen and spermatozoa. All three victims were bound hand and foot. Id. Approximately a year later, police arrested Charles Sanders in connection with the murders. Id. Sanders entered into a plea agreement, in which he pleaded guilty to three counts of second degree murder, admitted a gun enhancement, and agreed to cooperate with the prosecution, in exchange for a sentence of 17 years to life in prison. Id. During his interrogation by the police, Sanders gave both a tape-recorded and a written statement. Id. He also testified at Andrews’s trial, and described the crime as follows: Sanders testified that he and [Andrews] devised a plan to rob Wheeler, a drug dealer. [Andrews] armed himself with a .357 magnum and gave Sanders a .38-or .32-caliber automatic. On the evening of the murders, they visited their friend, Carol Brooks, who lived in the same apartment building as Wheeler, and then went to Wheeler’s apartment. In response to their knocking, Wheeler, who apparently knew [Andrews], let them in. Also inside the apartment was a woman (Patrice Brandon). After smoking some marijuana with Wheeler, [Andrews] and Sanders drew their guns. Sanders tied Wheeler and Brandon with belts and socks, put on a pair of gloves, and began to search the apartment for drugs and money. Except for some powder on a saucer which appeared to be cocaine, the search was unsuccessful. [Andrews] questioned Wheeler, who denied having any drugs or money. Saying he would make Brandon talk, [Andrews] dragged her into the kitchen and closed the door. Sanders remained in the living room with Wheeler. Sanders heard [Andrews] hitting Brandon and later heard sounds as though they were having sex. When [Andrews] came out of the kitchen shortly thereafter, Sanders saw Brandon’s pants around her ankles. [Andrews] put his gun in Wheeler’s mouth. He threatened to kill Wheeler and Brandon unless Wheeler revealed the location of the drugs. Wheeler said the ‘dope’ was in the attic, and pointed out a trap door leading up to it. Sanders climbed into the attic. While in the attic, Sanders heard two shots. When he came down, [Andrews] told him he had shot Wheeler because the latter had tried to jump out the window. Sanders asked if Wheeler was dead. [Andrews] responded he was ‘standing right up’ on Wheeler when he fired the gun.... When Sanders asked about Brandon, [Andrews] replied he had killed her before leaving the kitchen. While [Andrews] and Sanders were cleaning up the apartment, Ronald Chism knocked on the door and asked if everything was all right. [Andrews] said Wheeler was home and invited him inside. [Andrews] then hit Chism on the head, tied him up, and took him into the bathroom. Sanders saw [Andrews] sitting astride Chism’s back, joining and separating his clenched fists in a tugging motion, apparently strangling Chism. Sanders then saw [Andrews] go into the kitchen and choke Brandon with a wire clothes hanger. When the two left the apartment, [Andrews] gave Sanders some money, saying it was all he had found. In re Andrews, 28 Cal.4th 1234, 124 Cal.Rptr.2d 473, 52 P.3d 656, 658 (2002) (alterations, citations, and internal quotation marks omitted). Andrews was eventually arrested, and he was charged in June 1982. At trial, the jury heard Sanders’s testimony as well as the testimony of Carol Brooks. Brooks confirmed that Andrews and Sanders visited her on the night of the murders and told her about their plan to “get some money” from Wheeler. People v. Andrews, 260 Cal.Rptr. 583, 776 P.2d at 289. A week after the incident, Sanders told her about his involvement in the murders. Id. Then, a few weeks later, Andrews confessed to her that he shot Wheeler, had sex with Brandon, and took $300 during the robbery. Id. The prosecution also presented fingerprint evidence. Id. Police experts analyzed 50 prints lifted from the apartment; three prints belonged to Andrews. Id. One fingerprint was found on a coffee table in Wheeler’s living room. Id. Two palm prints were found on the kitchen floor, on either side of the spot where Brandon’s body was found, the left palm print being about a foot from her body. The defense primarily focused on undermining Sanders’s credibility. Id. Two jail inmates who had been incarcerated with Sanders testified. Id. They stated that, while Sanders was incarcerated with them, he made statements suggesting he planned to lie about the murders to shift blame onto Andrews and away from himself. Id. The jury deliberated for three days before finding Andrews guilty of murder. The jury also found three special circumstances to be true. Two special circumstances related to the offense conduct: (1) multiple murder and robbery murder, based on the murders of Wheeler, Brandon, and Chism, and the robbery of Wheeler, and (2) rape-murder, based on the rape and murder of Brandon. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 659. The third special circumstance was Andrews’s conviction for murder of a grocery store clerk in 1967. Id. Both the prosecutor and defense counsel made brief presentations at the penalty phase. The prosecutor presented evidence through a joint stipulation. Id. He noted that the jury had already found that Andrews had been convicted of murder in 1967. The parties also stipulated that Andrews had been convicted of armed robbery in May 1968, that he had been convicted of escape in November 1969, and that he had been convicted of robbery in June 1977. Id. The stipulation did not describe the facts of the offenses underlying these additional convictions. The prosecution also submitted photographs of the dead bodies of Patrice Brandon and Ronald Chism as they were found by the police in the apartment; the photos had been excluded at the guilt phase on the ground they were unduly inflammatory. Id. Finally, the parties stipulated that Andrews’s birth date was July 2,1950. Id. The defense evidence consisted of two sworn statements that were read to the jury. Id. The statements described facts underlying the incident in September 1966 that formed the basis of Andrews’s 1967 conviction for murder. According to the statements, Andrews and a 17-year-old companion, both of whom were armed, attempted to rob a grocery store, and the companion fired three shots, killing the grocery store clerk. Id. In his closing argument, defense counsel focused on mitigating circumstances. He argued that Andrews’s crimes were unsophisticated, occurred several years apart, and all involved the unexpected escalation of a planned robbery. Id. He pointed out that Andrews was only 15 years old at the time of the murder of the grocery store clerk, and was not the shooter. Id. He portrayed Andrews’s conduct as less blameworthy because the murders occurred while Andrews, Sanders, Wheeler, and Brandon were under the influence of illegal drugs. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 659-60. Finally, he emphasized that other murderers had received life without the possibility of parole despite the jury’s finding of special circumstances, and despite more blameworthy conduct. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 659. He pointed out that in this very case, Sanders received a sentence of only 17 years to life. Id. 124 Cal.Rptr.2d 473, 52 P.Sd at 660. The prosecution made no rebuttal. After one day of deliberations, the jury returned a verdict imposing the death penalty for each of the three murder counts. The court sentenced Andrews to death on the three counts on June 8, 1984. The California Supreme Court affirmed the conviction and sentence on direct appeal on August 3, 1989. People v. Andrews, 260 Cal.Rptr. 583, 776 P.2d at 285, 288. B Andrews filed petitions for state post-conviction relief, claiming, among other things, that his counsel’s assistance was ineffective at the penalty phase because counsel did not adequately investigate and present mitigating evidence. The California Supreme Court summarily, denied all of Andrews’s claims, except for his penalty phase ineffective assistance of counsel claim. The California Supreme Court appointed a referee to take evidence and make factual findings on six questions related to Andrews’s penalty phase ineffective assistance of counsel claim. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 659. Two of the six questions are relevant to the question of whether Andrews was prejudiced by his counsel’s allegedly ineffective assistance: “1. What mitigating character and background evidence could have been, but was not, presented by [Andrewsj’s trial attorneys at his penalty trial?” id. 124 Cal.Rptr.2d 473, 52 P.3d at 660, and “5. What evidence, damaging to [Andrews], but not presented by the prosecution at the guilt or penalty trials, would likely have been presented in rebuttal, if [Andrews] had introduced any such mitigating character and background evidence?” id. 124 Cal.Rptr.2d 473, 52 P.3d at 664. The referee received the testimony of over 50 witnesses, which took place over the span of six years, id. 124 Cal.Rptr.2d 473, 52 P.3d at 660, and issued a lengthy written report of her findings. The California Supreme Court denied Andrews’s penalty phase ineffective assistance of counsel claim in a lengthy opinion. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 656-76. In its opinion, the court summarized the referee’s findings. In response to the first question, the referee identified three broad categories of mitigating evidence that were available but not presented to the jury: Andrews’s family background; the conditions of his confinement in a juvenile reform school and in the Alabama prison system; and his mental health. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 660. As summarized in the court’s opinion, the referee’s report included the following information regarding Andrews’s background. When he was very young,,Andrews’s alcoholic parents separated, and his mother left him to be raised by his grandparents and aunt, in a large family home with his siblings and cousins, located in a poor, segregated neighborhood of Mobile, Alabama. Id. The referee described Andrews’s grandfather as “loving, benevolent, and responsible,” id., and the court added that Andrews’s mother regularly sent money and clothing to her children and that Andrews’s upbringing and early family life were “relatively stable and without serious privation or abuse,” id. 124 Cal.Rptr.2d 473, 52 P.3d at 670. When Andrews was around nine or ten, his mother returned home to stay. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 660, 670. She had children by another marriage, of whom Andrews was jealous. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 660. Around that time Andrews’s grandfather, a “pivotal figure” in his life, died. Id. (internal quotation marks omitted). Andrews became withdrawn, skipped school, and at age 14, committed car theft and was sent to a reform school known as Mt. Meigs, formally the Alabama Industrial School for Negro Children. Id. The conditions at Mt. Meigs, described succinctly by the state court as “appalling,” included “beatings, brutality, inadequate conditions and sexual predators.” Id. 124 Cal.Rptr.2d 473, 52 P.3d at 660-61 (internal quotation marks omitted). According to the referee’s, report, one witness described it as “a farming operation and a penal colony for children,” while others described “inhuman conditions, inadequate food and clothing and' severe beatings,” with “sticks, broom handles, tree limbs, and hoe handles ... or fan belts.” Andrews was released at age 16. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661. Within three months of his release, in September 1966, he and a companion were involved in the attempted robbery and murder of the grocery store clerk that became one of the three special circumstances in this capital case. See supra at 768; In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 661. The evidence showed that when Andrews and his companion were fleeing the scene in a taxi, they robbed the taxi driver at gunpoint. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 661. The taxi driver testified he heard Andrews say “[l]et’s shoot him.” Id. 124 Cal.Rptr.2d 473, 52 P.3d at 665 (internal quotation marks omitted). Andrews then fired at least two shots at the taxi driver. Id. In 1967, Andrews was convicted of murder based on the grocery store incident, and in 1968, he was convicted of armed robbery of the taxi driver. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661 n. 4. Just before he turned 18, he was committed to Alabama state prison. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661. Summarizing the referee’s findings about conditions in the four different prisons in which Andrews was confined over ten years, the California Supreme Court stated: [The referee] described conditions in these institutions as abysmal, characterized by severe overcrowding, racial segregation, substandard facilities, no separation of the tougher inmates from younger or smaller inmates, constant violence, the persistent threat of sexual assaults and the constant presence of sexual pressure, the availability and necessity of weapons by all inmates, and degrading conditions in disciplinary modules. [Andrews] not only received beatings but was also personally subjected to sexual assaults. Id. (internal quotation marks omitted). The court also noted that Andrews had been involved in prison violence, including “the stabbings of two inmates who had been threatening him.” Id. (internal quotation marks omitted). However, Andrews “was rarely the instigator of violence,” was “the prey rather than the predator” when he was involved, and was often a target of violence due to his small stature. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 662 (internal quotation marks omitted). He also “appeared to adjust well when the structure permitted and ... would continue to do so” and, “when circumstances permitted, he tended to hold positions of responsibility.” Id. After his release from prison in 1976, Andrews engaged in an attempted robbery of a laundry. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661. In this incident: Mobile Police Officer Pettis testified that on March 23, 1977, he responded to a robbery call. Entering the store from which the call came, he and other officers saw [Andrews] holding a crying young woman hostage with a cocked gun at her head. He told the officers to leave and “continued to repeat, ‘Someone’s going to get shot, I’m going to shoot.’” The officers withdrew. Ultimately, [Andrews] surrendered to the officers after releasing the young woman and another woman whom he had also held hostage. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 665. Andrews was arrested for the robbery, but escaped from jail and fled to California. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661. In California, Andrews met Debra Pickett, with whom he had a stable relationship. Id. The couple had a child, and Andrews held a job during this time. Id. But Andrews resumed using cocaine, left his job and family, and then committed the three murders at issue here. Id. The referee also described the testimony from mental health experts that could have been presented at the penalty phase. Summarizing the referee’s report, the California Supreme Court noted that the experts diagnosed Andrews with a range of mental disorders, including attention deficit disorder, post traumatic stress disorder (PTSD), and mild to moderate organic brain impairment, in part due to drug use and possibly due to a head injury in prison. Id. The experts opined that Andrews’s learning disability, the adverse circumstances of his childhood, the impact of the correctional systems, and the PTSD made his commission of the murders and sexual assault more understandable and less morally culpable. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661-62. The experts gave specific examples of how Andrews’s impairments and the brutal conditions of incarceration made it difficult for him to avoid getting into trouble with the law. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661-62, 670. For example, one psychiatrist testified that one of the victims had hurled an insulting slur at Andrews a few days before the murders, and Andrews’s PTSD would predispose him to overreact to the slur, which contributed to the expert’s conclusion that Andrews was “under the influence of extreme mental or emotional distress” when he committed the murders. In addressing the question whether the prosecutor would have introduced evidence damaging to Andrews in rebuttal, the referee found that the prosecution’s rebuttal presentation could have included evidence about two of Andrews’s prior convictions. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 664-65. First, during the penalty phase of Andrews’s trial, the jury was reminded of its special circumstance finding, that Andrews had been convicted of murder in 1967 for his involvement in the grocery store robbery-murder in 1966. It also heard that Andrews was convicted of robbery in 1968, but it did not hear the facts on which the conviction was based, such as evidence that Andrews shot at the driver of the getaway taxi, which could have been introduced as aggravating evidence. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 659, 664. The prosecution could have introduced that evidence to show Andrews’s greater moral culpability for the incident. Id. 124 Cal. Rptr.2d 473, 52 P.3d at 664. Second, the prosecution could have informed the jury about Andrews’s attempt to rob a laundry business following his release from prison in 1976, which involved holding two women hostage, one with a gun to her head. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 661, 665. Further, the referee determined that the prosecution could have called its own mental health experts to rebut Andrews’s evidence. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 665. The state could have presented expert testimony that Andrews did not suffer from PTSD, but rather suffered from antisocial personality disorder, resented authority, and had a normal-range IQ of 93. Id. A second expert would have testified that Andrews’s ability to hold a job and maintain a stable relationship with Debra Pickett before he committed the murders indicated he did not suffer from brain damage, and the planning and thought that went into the murders made it unlikely that he was under the influence of drugs at the time. Id. After recounting the referee’s findings on these questions as well as the other four questions, and resolving objections to the referee’s report, the California Supreme Court turned to its analysis of Andrews’s ineffective assistance of counsel claim. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 667. It held that Andrews’s counsel’s performance was not deficient during the penalty phase of the trial because Andrews’s counsel made a reasonable investigation, under then-existing professional norms and Supreme Court precedent, and counsel also made a reasonable decision not to conduct additional investigation. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 667-71. It then held that even if counsel’s performance were deficient, Andrews suffered no prejudice because a different result was not reasonably probable in light of the severity of his crimes, the fact that the jury might view some of his mitigating evidence as aggravating, and the substantial rebuttal evidence that could have been presented. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 671. Andrews filed a habeas petition in federal district court. His amended petition raised 32 claims, including multiple sub-claims. In a lengthy ruling on the merits of the petition, the district court denied 31 ■claims, but granted relief on the claim that Andrews’s counsel were ineffective at the penalty phase of his trial for failing to investigate and present additional mitigating evidence. Reviewing the evidence produced by the referee on this issue, the district court concluded that counsel had made “essentially no effort to investigate and put on evidence in mitigation,” which constituted deficient performance under Strickland. The court then ruled that counsel’s “failure to adequately investigate and discover evidence of a life filled with abuse and privation is sufficient to establish prejudice under Strickland,” but the court did not consider whether the California Supreme Court’s rejection of this ineffective assistance of counsel claim was “contrary to, or involved an unreasonable application of’ Strickland under 28 U.S.C. § 2254(d)(1). The court granted Andrews’s petition on this ineffective assistance of counsel claim, denied Andrews’s other 31 claims, and granted a certificate of appealability (COA) on Andrews’s claim that California’s lethal injection protocol violates the Eighth Amendment (Claim 25). Andrews timely appealed, challenging the district court’s denial of Claim 25 and the denials of several uncertified claims. The state cross-appealed the district court’s grant of relief on Andrews’s ineffective assistance of counsel claim. After briefing on his appeal was complete, Andrews moved for permission to brief an additional uncertified claim, in which he seeks habeas relief on the ground that it would violate the Eighth Amendment to execute him after a long delay from the date of his sentencing. We granted the motion. II We review a district court’s grant or denial of habeas relief de novo. Moses v. Payne, 555 F.3d 742, 750 (9th Cir.2009). A The Antiterrorism and Effective Death Penalty Act (AEDPA) applies to Andrews’s federal habeas petition, which was filed after April 24, 1996. See Lindh v. Murphy, 521 U.S. 320, 322, 336, 117 S.Ct. 2059, 138 L.Ed.2d 481 (1997). Under AEDPA, a court may not grant a habeas petition “with respect to any claim that was adjudicated on the merits in State court proceedings,” 28 U.S.C. § 2254(d), unless the state court’s judgment “resulted in a decision that was contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States,” § 2254(d)(1), or “was based on an unreasonable determination of the facts in light of the evidence presented in the State court proceeding,” § 2254(d)(2). Under § 2254(d)(1), the relevant Supreme Court precedent includes only the decisions in existence “as of the time the state court renders its decision.” Greene v. Fisher, — U.S.-, 132 S.Ct. 38, 44, 181 L.Ed.2d 336 (2011) (internal quotation marks and emphasis omitted); see also Cullen v. Pinholster, 563 U.S. 170, 131 S.Ct. 1388, 1399, 179 L.Ed.2d 557 (2011) (“State-court decisions are measured against [the Supreme] Court’s precedents as of the time the state court renders its decision.” (internal quotation marks omitted)). Thus, Supreme Court cases decided after the state court’s decision are not clearly established precedent under § 2254(d)(1) for purposes of evaluating whether the state court reasonably applied such precedent. A Supreme Court precedent is not clearly established law under § 2254(d)(1) unless it “squarely addresses the issue” in the case before the state court, Wright v. Van Patten, 552 U.S. 120, 125-26, 128 S.Ct. 743, 169 L.Ed.2d 583 (2008) (per curiam), or “establish[es] a legal principle that ‘clearly extends’ ” to the case before the state court, Moses, 555 F.3d at 754 (alterations omitted) (quoting Van Patten, 552 U.S. at 123, 128 S.Ct. 743); see also Carey v. Musladin, 549 U.S. 70, 76-77, 127 S.Ct. 649, 166 L.Ed.2d 482 (2006) (holding that Supreme Court cases evaluating state-sponsored courtroom conduct were not clearly established law governing private actor courtroom conduct). “[W]hen a state court may draw a principled distinction between the case before it and Supreme Court caselaw, the law is not clearly established for the state-court case.” Murdoch v. Castro, 609 F.3d 983, 991 (9th Cir.2010). “[I]f a habeas court must extend a rationale before it can apply to the facts at hand, then by definition the rationale was not clearly established at the time of the state-court decision.” White v. Woodall, — U.S. -, 134 S.Ct. 1697, 1706, 188 L.Ed.2d 698 (2014) (internal quotation marks omitted). A principle is clearly established law governing the case “if, and only if, it is so obvious that a clearly established rule applies to a given set of facts that there could be no fair-minded disagreement on the question.” Id. at 1706-07 (internal quotation marks omitted). A state court decision is “contrary to” Supreme Court precedent if “the state court applies a rule that contradicts the governing law set forth in [Supreme Court] cases.” Williams v. Taylor, 529 U.S. 362, 405, 120 S.Ct. 1495, 146 L.Ed.2d 389 (2000). An “unreasonable application” of Supreme Court precedent is not one that is merely “incorrect or erroneous,” Lockyer v. Andrade, 538 U.S. 63, 75, 123 S.Ct. 1166, 155 L.Ed.2d 144 (2003); see also Williams, 529 U.S. at 410, 120 S.Ct. 1495; rather, “[t]he pivotal question is whether the state court’s application of the [relevant Supreme Court precedent] was unreasonable,” Harrington v. Richter, 562 U.S. 86, 101, 131 S.Ct. 770, 178 L.Ed.2d 624 (2011) (emphasis added). If “ ‘fair-minded jurists could disagree’ on the correctness of the state court’s decision,” that decision is not unreasonable. Id. at 101, 131 S.Ct. 770 (quoting Yarborough v. Alvarado, 541 U.S. 652, 664, 124 S.Ct. 2140, 158 L.Ed.2d 938 (2004)). A state court summary denial is an “unreasonable application” of Supreme Court precedent only if “there was no reasonable basis,” id. at 98, 131 S.Ct. 770, for the decision in light of the “arguments or theories [that] ... could have supported[] the state court’s decision,” id. at 102,131 S.Ct. 770. The Supreme Court has made clear that § 2254(d) sets forth a “highly deferential standard[,] ... which demands that state-court decisions be given the benefit of the doubt.” Pinholster, 131 S.Ct. at 1398 (internal quotation marks omitted). “As amended by AEDPA, § 2254(d) stops short of imposing a complete bar on federal-court relitigation of claims already rejected in state proceedings,” but only “preserves authority to issue the writ in cases where there is no possibility fairminded jurists could disagree that the state court’s decision conflicts with this Court’s precedents” and “goes no further.” Richter, 562 U.S. at 102, 131 S.Ct. 770. “[E]ven a strong case for relief does not mean the state court’s contrary conclusion was unreasonable.” Id. In a nutshell, “[i]f this standard is difficult to meet, that is because it was meant to be.” Id. at 102, 131 S.Ct. 770. B The clearly established federal law for ineffective assistance of counsel claims, as determined by the Supreme Court, is Strickland v. Washington, 466 U.S. 668, 104 S.Ct. 2052, 80 L.Ed.2d 674 (1984), and its progeny. See Pinholster, 131 S.Ct. at 1403. Strickland concluded that, under the Sixth Amendment, the accused has the right to the effective assistance of counsel at trial and during capital sentencing proceedings. 466 U.S. at 684-87, 104 S.Ct. 2052. A petitioner claiming ineffective assistance of counsel must prove: (1) that “counsel’s performance was deficient,” and (2) that “the deficient performance prejudiced the defense.” Id. at 687, 104 S.Ct. 2052. “[A] court need not determine whether counsel’s performance was deficient before examining the prejudice suffered by the defendant as a result of the alleged deficiencies.” Id. at 697, 104 S.Ct. 2052. Rather, “[i]f it is easier to dispose of an ineffectiveness claim on the ground of lack of sufficient prejudice, which we expect will often be so, that course should be followed.” Id. In short, a court need not address the two Strickland prongs in order; if ruling on the prejudice prong more efficiently resolves the case, reaching the deficiency prong is unnecessary. Id. In determining whether a state court’s adjudication of an ineffective assistance of counsel claim was an unreasonable application of Supreme Court precedent, we may consider how the Supreme Court itself has applied Strickland to other factual contexts, but this is merely “illustrative of the proper application of [Strickland’s] standards.” See Wiggins v. Smith, 539 U.S. 510, 522, 123 S.Ct. 2527, 156 L.Ed.2d 471 (2003); see also Pinholster, 131 S.Ct. at 1407 n. 17; Brian R. Means, Federal Habeas Manual § 3:29 (2014). The Supreme Court has warned us not to derive “strict rules” from its cases applying Strickland de novo because “the Strickland test ‘of necessity requires a case-by-case examination of the evidence.’ ” Pin-holster, 131 S.Ct. at 1407 & n. 17 (quoting Williams, 529 U.S. at 391, 120 S.Ct. 1495). Further, Supreme Court cases decided on de novo review “offer no guidance with respect to whether a state court has unreasonably determined that prejudice is lacking” or defense counsel was deficient, and so are not directly applicable to a federal court’s review under § 2254(d)(1) of a habeas petitioner’s claim that a state court unreasonably applied Strickland. Id. at 1411. Indeed, a state court’s application of Strickland may be objectively reasonable- based on clearly established Supreme Court precedent at the time of its decision even if the Supreme Court’s subsequent applications of Strickland suggest a different result. By contrast, when the Supreme Court addresses the AEDPA question whether a state court’s adjudication of an ineffective assistance of counsel claim was an unreasonable application of Strickland, its reasoning guides a federal court’s AEDPA analysis regardless of when the opinion was issued. The Supreme Court has provided guidance for applying Strickland to determine whether counsel’s “deficient performance prejudiced the defense,” Strickland, 466 U.S. at 687, 104 S.Ct. 2052, at the penalty phase of a capital case. To make this prejudice determination, a court generally proceeds through three steps: (1) evaluating and weighing the totality of the available mitigation evidence, see Williams, 529 U.S. at 397-98, 120 S.Ct. 1495; Pinholster, 131 S.Ct. at 1408-10; (2) evaluating and weighing the aggravating evidence and any rebuttal evidence that could have been adduced by the government had the mitigating evidence been introduced, Williams, 529 U.S. at 397-98, 120 S.Ct. 1495; Pin-holster, 131 S.Ct. at 1408-10, and (3) reweighing the evidence in aggravation against the totality of available mitigating evidence, see Sears v. Upton, 561 U.S. 945, 955-56, 130 S.Ct. 3259, 177 L.Ed.2d 1025 (2010) (per curiam); Wiggins, 539 U.S. at 534, 123 S.Ct. 2527; Williams, 529 U.S. at 397-98, 120 S.Ct. 1495, to determine “whether there is a reasonable probability that, absent the errors, the sentencer ... would have concluded that the balance of aggravating and mitigating circumstances did not warrant death,” Strickland, 466 U.S. at 695, 104 S.Ct. 2052. We explain the Supreme Court’s guidance on each of these steps. 1 The first step in determining whether counsel’s deficient performance prejudiced the defendant at the penalty phase is evaluating “the totality of the available mitigation evidence.” Williams, 529 U.S. at 397-98, 120 S.Ct. 1495. The evidence to be evaluated includes both evidence that was actually presented at sentencing and evidence that a competent attorney would have introduced. See Wiggins, 539 U.S. at 534-35, 123 S.Ct. 2527. We may assume that a competent attorney would have considered presenting all of the evidence adduced in post-conviction proceedings. See Wong v. Belmontes, 558 U.S. 15, 20, 130 S.Ct. 383, 175 L.Ed.2d 328 (2009) (per curiam). Mitigation evidence is a broad category, as a jury must be permitted to consider all' relevant mitigating factors. Lockett v. Ohio, 438 U.S. 586, 608, 98 S.Ct. 2954, 57 L.Ed.2d 973 (1978) (plurality opinion); Eddings v. Oklahoma, 455 U.S. 104, 110-12, 102 S.Ct. 869, 71 L.Ed.2d 1 (1982). The Supreme Court has identified several non-exclusive categories of mitigation evidence, focusing primarily on evidence that aids the jury’s evaluation of a defendant’s moral culpability. See Wiggins, 539 U.S. at 535, 123 S.Ct. 2527. For instance, evidence of a defendant’s disadvantaged background may lead a jury to conclude the defendant is “less culpable than defendants who have no such excuse.” Penry v. Lynaugh, 492 U.S. 302, 319, 109 S.Ct. 2934, 106 L.Ed.2d 256 (1989) (internal quotation marks omitted), abrogated on other grounds by Atkins v. Virginia, 536 U.S. 304, 122 S.Ct. 2242, 153 L.Ed.2d 335 (2002). Thus, a defendant who had a childhood “filled with abuse and privation,” including being raised by parents who were eventually imprisoned for criminal child neglect, could influence a jury’s appraisal of the defendant’s moral culpability. Williams, 529 U.S at 395, 398, 120 S.Ct. 1495; see also Wiggins, 539 U.S. at 535, 123 S.Ct. 2527 (mitigating evidence included evidence that the defendant suffered severe privation and abuse as a child, had an alcoholic and absent mother, was physically and sexually abused in foster care, and was homeless for a brief period); Rompilla v. Beard, 545 U.S. 374, 391-93, 125 S.Ct. 2456, 162 L.Ed.2d 360 (2005) (mitigating evidence included evidence that the defendant was raised in a slum by severely abusive, alcoholic parents, who did not provide for him and isolated him). Similarly, evidence of a defendant’s mental or emotional difficulties may lead a jury to conclude that a defendant is less culpable than defendants without such difficulties. Penry, 492 U.S. at 319,109 S.Ct. 2934. For instance, evidence that a defendant is “borderline mentally retarded,” Williams, 529 U.S. at 396, 120 S.Ct. 1495 (internal quotation marks omitted), or has severe PTSD from military combat, see Porter v. McCollum, 558 U.S. 30, 35-36 & n. 4, 43-44, 130 S.Ct. 447, 175 L.Ed.2d 398 (2009), or has severe learning and behavioral disabilities, frontal lobe injuries, and brain damage from drug and alcohol abuse, see Sears, 561 U.S. at 948-49, 130 S.Ct. 3259, is potentially mitigating evidence. Evidence of conduct or behavior demonstrating the defendant’s good character may also be mitigating. In Williams, the Court gave weight to evidence that the defendant had turned himself in, alerted police to a previously undetected crime, expressed remorse, cooperated with police, and behaved well in prison. 529 U.S. at 369, 396, 398, 120 S.Ct. 1495. In Belmontes, the Court noted mitigation evidence that the defendant had maintained strong relationships with family members in spite of his terrible childhood, and that while in prison, he assisted others through a prison religious .program and rose to second in command in a fire crew. 558 U.S. at 21,130 S.Ct. 383. After identifying the evidence that the petitioner claims to be mitigating, a court must weigh its strength by assessing its likely impact on a jury. This weighing process includes evaluating whether its impact on the jury might be aggravating rather than mitigating. See Pinholster, 131 S.Ct. at 1410. The Supreme Court has indicated that courts can consider the fact that mitigation “may be in the eye of the beholder,” and juries may find that some evidence offered as mitigation cuts the other way. Burger v. Kemp, 483 U.S. 776, 794, 107 S.Ct. 3114, 97 L.Ed.2d 638 (1987) (alterations and internal quotation marks omitted). In Burger, the Court noted that “[o]n one hand, a jury could react with sympathy over the tragic childhood” of the defendant, while on the other hand, the same testimony could establish the defendant’s “unpredictable propensity for violence” that resulted in murder. Id. (internal quotation marks omitted). Similarly, evidence of mental and emotional problems might suggest an increased likelihood that a defendant would be dangerous in the future. See Pinholster, 131 S.Ct. at 1410 (noting that evidence of the defendant’s family background, their substance abuse, and their mental health issues, was “by no means clearly mitigating, as the jury might have concluded that [the defendant] was simply beyond rehabilitation”). The Court has also observed that evidence of the defendant’s normal youth might, in the jury’s eyes, establish greater moral culpability on the part of the defendant. See Bell v. Cone, 535 U.S. 685, 701-02, 122 S.Ct. 1843, 152 L.Ed.2d 914 (2002). 2 The second step in determining whether counsel’s deficient performance prejudiced the defendant at the penalty phase is evaluating the weight of the aggravating evidence and any rebuttal evidence that could have been adduced by the government had the mitigating evidence been introduced. See Williams, 529 U.S. at 397-98, 120 S.Ct. 1495; Pinholster, 131 S.Ct. at 1408-10. Aggravating evidence may include evidence relating to the circumstances of the crime. Thus in Strickland, the Court found the aggravating evidence to be “overwhelming” where the defendant had repeatedly stabbed the three murder victims during a robbery. 466 U.S. at 674, 700, 104 S.Ct. 2052. Similarly, where the record showed that the defendant had bludgeoned a woman to death with 15 to 20 blows of a steel dumbbell bar to steal goods worth a mere $100, the Supreme Court agreed with the state court that the aggravating evidence was “simply overwhelming” and determined that counsel’s failure to introduce certain mitigating evidence was not prejudicial. Belmontes, 558 U.S. at 15-16, 26-27, 130 S.Ct. 383 (internal quotation marks omitted). In Bobby v. Van Hook, the Supreme Court gave weight to evidence that the murder was committed in the course of a scheme to rob homosexual men by luring them into secluded settings. 558 U.S. 4, 12-13,130 S.Ct. 13,175 L.Ed.2d 255 (2009) (per curiam). In doing so, the Court clarified that the weight, not the number, of the aggravating factors was important. Id. Evidence about a defendant’s pri- or criminal history is also aggravating and can be introduced in rebuttal, and a severe criminal history carries great weight. See Woodford v. Visciotti, 537 U.S. 19, 26-27, 123 S.Ct. 357, 154 L.Ed.2d 279 (2002) (criminal history that included “the knifing of one man, and the stabbing of a pregnant woman as she lay in bed trying to protect her unborn baby,” combined with the circumstances of the crime, was “overwhelming” and “devastating” aggravating evidence); accord Bell, 535 U.S. at 700 & n. 5, 122 S.Ct. 1843 (defense counsel reasonably feared the prosecution would elicit information about defendant’s criminal history, which included robberies, in rebuttal); Burger, 483 U.S. at 793, 107 S.Ct. 3114 (defense counsel reasonably feared the prosecution would introduce the defendant’s juvenile criminal history in rebuttal, when he had a clean adult record). Evidence that a defendant had previously committed another. murder may be “the most powerful imaginable aggravating evidence.” Belmontes, 558 U.S. at 28, 130 S.Ct. 383 (internal quotation marks omitted). Rebuttal evidence may also directly undermine the value of the mitigation evidence. For example, the Supreme Court noted in Pinholster that it would be “of questionable mitigating value” for defense counsel to introduce expert testimony diagnosing a defendant with bipolar mood disorder and seizure disorders, because such evidence would invite rebuttal by a state expert, who could reject the diagnosis of bipolar disorder and offer a different diagnosis of antisocial personality disorder. Pinholster, 131 S.Ct. at 1396,1410. 3 Finally, the third step in determining whether counsel’s 'deficient performance prejudiced the defendant at the penalty phase is to “reweigh the evidence in aggravation against the totality of available mitigating evidence,” Wiggins, 539 U.S. at 534, 123 S.Ct. 2527, in order to determine “whether there is a reasonable probability that, absent the errors, the sentencer ... would- have concluded that the balance of aggravating and mitigating circumstances did not warrant death,” Strickland, 466 U.S. at 695,104 S.Ct. 2052. A “reasonable probability” is a level of probability that “undermine[s] confidence in the outcome.” Id. at 694, 104 S.Ct. 2052. However, counsel’s deficient performance is not prejudicial merely because the court cannot “rule out” the possibility that the sentencer would have imposed a sentence of life in prison instead of the death penalty. Belmontes, 558 U.S. at 20, 27, 130 S.Ct. 383 (internal quotation marks omitted); see also Richter, 562 U.S. at 111, 131 S.Ct. 770 (“In assessing prejudice under Strickland, the question is not whether a court can be certain counsel’s performance had no effect on the outcome....”). Rather, “[t]he likelihood of a different result must be substantial, not just conceivable.” Richter, 562 U.S. at 112, 131 S.Ct. 770 (citing Strickland, 466 U.S. at 693, 104 S.Ct. 2052). Thus, “the difference between Strickland’s prejudice standard and a more-probable-than-not standard is slight and matters ‘only in the rarest case.’ ” Id. (quoting Strickland, 466 U.S. at 697,104 S.Ct. 2052). The Court has found a reasonable probability of a different outcome when only scant and weak aggravating evidence could have been presented in rebuttal to strongly mitigating evidence. See Wiggins, 539 U.S. at 534-36, 537-38, 123 S.Ct. 2527 (holding that there was a reasonable probability that the jury would have reached a different result at sentencing had it heard powerful mitigating evidence regarding the defendant’s childhood background, when the state could have presented only weak rebuttal evidence). By contrast, the Court has found no prejudice when the aggravating evidence is overwhelming, even though the mitigating evidence is strong. See Visciotti, 537 U.S. at 26-27, 123 S.Ct. 357 (holding that there was no reasonable probability of a different result when the mitigating evidencé, including the defendant’s “troubled family background” and possible seizure disorder, did not outweigh the “overwhelming” aggravating factors, including the circumstances of the crime and potential rebuttal evidence of prior offenses). In reweighing aggravating and mitigating evidence, the Court has also examined whether mitigating evidence would be merely cumulative or would have significantly altered the information provided to the sentencer. See Strickland, 466 U.S. at 699N00, 104 S.Ct. 2052; Porter, 558 U.S. at 41-42, 130 S.Ct. 447. In Strickland, the new information “would barely have altered” the picture presented at sentencing, and the Court found no prejudice. 466 U.S. at 699-700,104 S.Ct. 2052. Similarly, in Belmontes, the Court concluded that merely cumulative evidence regarding a petitioner’s difficult childhood, and expert testimony regarding a petitioner’s mental state “seeking to explain his behavior, or putting it in some favorable context” would not outweigh the facts of a brutal murder, and would be even less likely to outweigh evidence that the defendant had committed a prior murder. 558 U.S. at 22-24, 27-28, 130 S.Ct. 383. Accordingly, the Court concluded that any failure of counsel to present additional mitigating evidence was not prejudicial. Id. at 27,130 S.Ct. 383. These Supreme Court opinions suggest that under Strickland’s prejudice prong, cumulative mitigating evidence does not support a conclusion that there would be a reasonable probability of a different outcome. New mitigating evidence can support such a conclusion only if it is sufficiently strong, and the known or additional aggravating evidence is not overwhelming. C In light of this guidance, we now evaluate the California Supreme Court’s rejection of Andrews’s claim that he was prejudiced by his counsel’s failure to investigate and present additional mitigating evidence at the penalty phase of his trial. We must determine whether this decision was “contrary to, or involved an unreasonable application of,” Strickland or other Supreme Court precedent in existence at the time of its opinion. § 2254(d)(1); see Pinholster, 131 S.Ct. at 1399. In considering whether any deficiency by Andrews’s counsel was prejudicial, the California Supreme Court correctly followed Strickland in asking whether, even if counsel was deficient, Andrews’s defense was not prejudiced by any such deficiency because a different result was not reasonably probable. See In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 671 (quoting Strickland, 466 U.S. at 694, 104 S.Ct. 2052). The California Supreme Court then reasonably carried out the three steps indicated by Supreme Court opinions for evaluating prejudice at the penalty phase. 1 The court first considered the totality of the mitigating evidence presented at trial, as well as what mitigation could have been presented by a competent attorney, based on the six-year review and report by the referee. See Williams, 529 U.S. at 397-98, 120 S.Ct. 1495. The court reviewed all of the mitigating evidence that Andrews presented, including Andrews’s family background, In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 660, 670, incarceration in Mt. Meigs and in Alabama prisons, id. 124 Cal.Rptr.2d 473, 52 P.3d at 660-61, 670-71, and mental health evidence, id. 124 Cal.Rptr.2d 473, 52 P.3d at 661-62, 670, observing that the similar types of mitigating evidence have been considered in Supreme Court precedent, id. 124 Cal.Rptr.2d 473, 52 P.3d at 672-75; see Penry, 492 U.S. at 319, 109 S.Ct. 2934; Williams, 529 U.S. at 395-98, 120 S.Ct. 1495. The California Supreme Court then evaluated the strength of this mitigating evidence by considering, among other things, whether it might be viewed by a jury as aggravating. See Burger, 483 U.S. at 793, 107 S.Ct. 3114; Pinholster, 131 S.Ct. at 1410. It reasonably concluded that much of the evidence identified as mitigating “was not conclusively and unambiguously mitigating,” and it evaluated the possibility that the evidence could be rebutted or used to Andrews’s disadvantage, or that cross examination might “deflate the mitigating impact” of the evidence. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 670 & n. 9. The court reasonably observed that a jury could have determined that Andrews’s family background did not reduce his moral culpability, given that Andrews was raised in a non-abusive, stable family situation. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 670; cf. Bell, 535 U.S. at 701-02, 122 S.Ct. 1843 (suggesting that evidence of a normal youth might “cut the other way”). The court reasonably concluded that “[Andrews] did not suffer a home environment that would place his crimes in any understandable context or explain his resorting to crime every time he was released or escaped from prison.” Id. 124 Cal.Rptr.2d 473, 52 P.3d at 670. In addition, the state court reasonably determined that the evidence regarding the prison conditions was double-edged. On the one hand, the prison conditions evidence left it in “no doubt [that Andrews] endured horrifically demeaning and degrading circumstances.” Id. On the other hand, the evidence would be presented primarily through the testimony of Andrews’s former fellow inmates, who had serious criminal records that could “draw[ ] an unfavorable comparison” with Andrews. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 671. “Many had themselves engaged in brutality while in prison and escaped with some frequency,” also similar to Andrews. Id. Moreover, no matter how the prison conditions evidence was presented, “[r]ather than engendering sympathy, the evidence could well have reinforced an impression of him as a person who had become desensitized and inured to violence and disrespect for the law.” Id.; cf. Pinholster, 131 S.Ct. at 1410. 2 After assessing the weight of the mitigating evidence and its likely impact on a jury, the state court followed Supreme Court guidance by turning to evaluate the weight of the aggravating evidence at trial, as well as any additional rebuttal evidence that could have been introduced. See Williams, 529 U.S. at 397-98, 120 S.Ct. 1495; Belmontes, 558 U.S. at 20, 24-28, 130 S.Ct. 383. Consistent with Supreme Court precedent, the state court considered the circumstances of Andrews’s crime and the nature of his prior criminal history. Turning to the circumstances of the crimes, the state court stated that the murders showed a “callous disregard for human life.” In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 671; cf. Strickland, 466 U.S. at 674, 700, 104 S.Ct. 2052; Belmontes, 558 U.S. at 15, 26-27, 130 S.Ct. 383. Andrews did not impulsively react to a situation that got out of hand; rather, he interacted with the victims in a calm and normal manner before torturing and killing them. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 671. He also did more than simply kill the victims. He raped and sodomized Brandon before murdering her, and he also murdered Wheeler and Chism with “considerable violence and evident sangfroid.” Id. The state court also eonsidered that, as rebuttal evidence, the prosecution could have presented the details of Andrews’s criminal history, cf. Bell, 535 U.S. at 700 & n. 5, 122 S.Ct. 1843; Burger, 483 U.S. at 793, 107 S.Ct. 3114, from which the jury might conclude Andrews was “aggressive and desensitized to violence,” In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 669. The jury might also have concluded that this “pattern of criminality” showed Andrews “would pose a danger to others if he were sentenced to life imprisonment.” Id. Also, the references to Andrews’s multiple escapes from prison might have been “inflammatory.” Id. Finally, the state court reasonably concluded that the prosecution could have presented its own mental health experts in rebuttal, and could have used the mental health evidence to Andrews’s disadvantage on cross examination. Id. 124 Cal.Rptr.2d 473, 52 P.3d at 670. The court noted the referee’s findings that prosecution experts could have testified that Andrews had normal intelligence and did not suffer brain damage, but had antisocial personality traits. Id.; cf. Pinholster, 131 S.Ct. at 1396, 1410. Nor was the state court unreasonable in concluding that Andrews’s experts’ testimony could backfire. For instance, the court noted that the “compelling” testimony from one of Andrews’s expert psychiatric witnesses, opining that Andrews’s prison experience caused him to react with rage to perceived insults, could cause a jury to conclude that Andrews “was unable to control lethal impulses on the slightest provocation.” In re Andrews, 124 Cal.Rptr.2d. 473, 52 P.3d at 670; cf. Pinholster, 131 S.Ct. at 1410. Finally, the presentation of the mental health evidence would have given the prosecutor additional opportunities to repeat the circumstances of these crimes as well as Andrews’s past criminality. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 670. 3 After evaluating the mitigating and aggravating evidence, the state court reweighed it and assessed whether it was reasonably probable that, in the absence of any deficient performance by counsel, the sentencer “would have concluded that the balance of aggravating and mitigating cir.eumstances did not warrant death.” Strickland, 466 U.S. at 695, 104 S.Ct. 2052; see In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 671-75. The state court applied the relevant Supreme Court precedent, and concluded that Andrews was not “prejudiced by counsel’s rejection of a defense premised on evidence of [AndrewsJ’s upbringing, the Alabama prison conditions he experienced, and his mental health in light of the circumstances of the crimes, given the ambiguous nature of some mitigating evidence and the substantial potential for damaging rebuttal.” Id. 124 Cal.Rptr.2d 473, 52 P.3d at 671. Relying on the Supreme Court’s decisions in Williams and Porter, Andrews argues that the California Supreme Court’s decision on the issue of prejudice was an unreasonable application of Strickland. In Williams, the Supreme Court held that the state court applied the wrong legal standard, 529 U.S. at 395-97, 120 S.Ct. 1495, and so applied Strickland de novo to the facts of that case, id. at 397-98, 120 S.Ct. 1495; see also Pinholster, 131 S.Ct. at 1410-11. The state court here discussed Williams at length and reasonably distinguished it as having “substantially dissimilar facts.” In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 675. In Williams, for instance, the defense counsel could have introduced strong character evidence, 529 U.S. at 398, 120 S.Ct. 1495, but no comparable evidence of good character was present in Andrews’s case. The defendant’s “nightmarish childhood” in Williams, 529 U.S. at 395, 398, 120 S.Ct. 1495, was far worse than Andrews’s relatively stable family background, see In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 674. The defendant in Williams was “borderline mentally retarded,” 529 U.S. at 396, 398, 120 S.Ct. 1495 (internal quotation marks omitted), while the prosecution could have presented evidence that Andrews was not mentally impaired, but rather had antisocial personality traits, In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 670. The only rebuttal evidence in Williams was the defendant’s three juvenile convictions, 529 U.S. at 396, 120 S.Ct. 1495, compared to Andrews’s robbery-murder, hostage taking, and history of escape from prison, In re Andrews, 124 Cal. Rptr.2d 473, 52 P.3d at 675. Finally, the circumstances of the crime in Williams were less brutal than Andrews’s triple murder, id., because the defendant in Williams killed the severely inebriated victim with one blow each to the chest and back after an argument, 529 U.S. at 367-68 & n. 1,120 S.Ct. 1495. Because the facts of Williams are dissimilar, the Supreme Court’s determination in Williams that counsel’s ineffective assistance was prejudicial does not make the state court’s contrary conclusion here unreasonable. See Richter, 562 U.S. at 101-02, 131 S.Ct. 770; see also Pinholster, 131 S.Ct. at 1410-11. Andrews also argues that the state court’s decision was unreasonable in light of Porter. Although Porter was decided years after the California Supreme Court’s opinion in this case, we give it careful consideration, because it provides direction for determining under AEDPA what constitutes an unreasonable application of Strickland. In Porter, the Supreme Court faulted the state court for failing to consider all of the mitigating evidence regarding the defendant’s family background, military service, and mental health issues. For instance, the state court entirely discounted the effect that evidence of the defendant’s brain abnormality and cognitive defects might have on a jury. See Porter, 558 U.S. at 42-44, 130 S.Ct. 447. Further, the state court unreasonably discounted mitigating evidence of childhood abuse and the defendant’s long record of military service. Id. at 43-44, 130 S.Ct. 447. Applying AEDPA, Porter held that the state court had unreasonably applied Strickland when it held that counsel’s failure to introduce this substantial mitigation evidence was not prejudicial. Id. at 44, 130 S.Ct. 447. The state court’s determinations in Porter are not closely analogous to the state court’s determinations in this case. Unlike the state court in Porter, the state court here considered all mitigation evidence in the record and did not fail to consider or “discount to irrelevance” significant evidence. See Porter, 558 U.S. at 43, 130 S.Ct. 447. The mitigation evidence in Porter, including that the defendant served in “horrific” battles of the Korean War, suffered childhood physical abuse, and had a brain abnormality, see id. at 41,130 S.Ct. 447, is less subject to rebuttal than the mitigation evidence in this case, see In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 670-71. Unlike here, where the state’s mental health expert disagreed with the defense experts’ conclusions and added a diagnosis of antisocial personality disorder, see id. 124 Cal.Rptr.2d 473, 52 P.3d at 670, in Porter, state experts could not rule out the defense experts’ mental health diagnosis, and the state court erred by failing to consider this evidence at all, see 558 U.S. at 36, 42-43, 130 S.Ct. 447. Likewise, evidence that the defendant had gone AWOL did not diminish evidence of his military service to “inconsequential proportions,” because our nation has a tradition of “according leniency to veterans,” and the evidence was “consistent with [the] theory of mitigation and [did] not impeach or diminish the evidence of his service.” Id. at 43-44, 130 S.Ct. 447 (internal quotation marks omitted). Here, by contrast, the state court found that Andrews “endured horrifically demeaning and degrading circumstances” in prison before acknowledging this evidence was “double-edged,” because it would also bring before the jury Andrews’s history of violence both in and out of prison and his escapes, which would be emphasized by their similarity to many of the witnesses who would testify for him. In re Andrews, 124 Cal.Rptr.2d 473, 52 P.3d at 670-71. Further, while the state court here reasonably determined that the prosecution could introduce damaging aggravating evidence, id. 124 Cal.Rptr.2d 473, 52 P.3d at 671, 675, in Porter, the Supreme Court held that the amount of aggravating evidence would be reduced, because one of the aggravating factors was invalid, 558 U.S. at 42, 130 S.Ct. 447. Because Porter is factually distinct from this case, it has little bearing on the question whether the state court unreasonably applied the prejudice prong of Strickland, Visciotti another Supreme Court case that provides direction for determining under AEDPA what constitutes an unreasonable application of Strickland, is more closely on point. In Visciotti the Supreme Court considered a state court’s rejection of a defendant’s Strickland claim. 537 U.S. at 26, 123 S.Ct. 357. The state court had weighed the mitigating evidence, including the defendant’s brain damage, difficult family background, and possible seizure disorder, against the aggravating factors, including the circumstances of the crime (the cold-blooded killing of two victims during a robbery) and his criminal history of knifing a man and stabbing a pregnant woman in bed “trying to protect her unborn baby,” and concluded that the defendant had suffered no prejudice. See id. at 25-26, 123 S.Ct. 357.' After the defendant filed a habeas petition, the district court granted relief and we affirmed. We reasoned that counsel’s deficient performance was prejudicial, because the “aggravating factors were not overwhelming.” Id. at 21-22, 25, 123 S.Ct. 357 (quoting Visciotti v. Woodford, 288 F.3d 1097, 1118 (9th Cir.2002)). The Supreme Court rever