In Porter v. McCollum, 558 U.S. 30 (2009), the United States Supreme Court held that the failure of trial counsel to conduct a thorough investigation into potential mitigation evidence for the penalty phase was prejudicial to the defendant. See id. The High Court held that the failure of trial counsel to investigate certain mitigation evidence undermined the outcome of the penalty phase proceedings because the absence of that evidence deprived the jury of the opportunity to consider any relevant mitigating evidence when it determined its recommended sentence. See id. The United States Supreme Court held in Porter v. McCollum(2009), that the Florida Supreme Court made an unreasonable application of Strickland when it concluded that Porter was not prejudiced by counsel's failure to investigate and present certain mitigation, including mental mitigation disclosed at Porter's postconviction evidentiary hearing. In addition to a brain abnormality, Porter had difficulty reading and writing, and limited schooling. Porter also had a childhood history of physical abuse. Id. at 454. The Supreme Court concluded: "We do not require a defendant to show 'that counsel's deficient conduct more likely than not altered the outcome' of his penalty proceeding, but rather that he establish 'a probability sufficient to undermine confidence in that outcome.' Strickland, 466 U.S. at 693-694, 104 S. Ct. 2052. This Porter has done." Porter, 130 S. Ct. 455-56. The Court held that a defendant need not show "'that counsel's deficient conduct more likely than not altered the outcome' of his potential proceeding, but rather that he establish 'a probability sufficient to undermine confidence in that outcome.'" The defendant "must show that but for his counsel's deficiency, there is a reasonable probability he would have received a different sentence. To assess that probability, we consider 'the totality of the available mitigation evidence--both that adduced at trial, and the evidence adduced in the postconviction proceeding'--and 'reweigh it against the evidence in aggravation.'" The Court explained: "To assess the probability of a different outcome under Strickland, we consider the totality of the available mitigation evidence-both that adduced at trial, and the evidence adduced in the habeas proceeding-and reweigh it against the evidence in aggravation." 558 U.S., at 41 (internal quotation marks omitted; third alteration in original). That same standard applies-and will necessarily require a court to "speculate" as to the effect of the new evidence-regardless of how much or how little mitigation evidence was presented during the initial penalty phase. Indeed, it is exactly this kind of probing inquiry that Justice SCALIA now undertakes, post, at 3268-3271, and that the trial court failed to do. In all circumstances, this is the proper prejudice standard for evaluating a claim of ineffective representation in the context of a penalty phase mitigation investigation. (Porter, 558 U.S. at 41). Indeed, in considering the mental mitigation presented at Porter's postconviction evidentiary hearing, the United States Supreme Court noted: The Florida Supreme Court either did not consider or unreasonably discounted the mitigation evidence adduced in the postconviction hearing. Under Florida law, mental health evidence that does not rise to the level of establishing a statutory mitigating circumstance may nonetheless be considered by the sentencing judge and jury as mitigating. See, e.g., Hoskins v. State, 965 So. 2d 1, 17-18 (Fla. 2007) (per curiam). Indeed, the Constitution requires that "the sentencer in capital cases must be permitted to consider any relevant mitigating factor." Eddings v. Oklahoma, 455 U.S. 104, 112, 102 S. Ct. 869, 71 L. Ed.2d 1 (1982). Yet neither the postconviction trial court nor the Florida Supreme Court gave any consideration for the purpose of nonstatutory mitigation to Dr. Dee's testimony regarding the existence of a brain abnormality and cognitive defects. While the State's experts identified perceived problems with the tests that Dr. Dee used and the conclusions that he drew from them, it was not reasonable to discount entirely the effect that his testimony might have had on the jury or the sentencing judge. (Porter, 130 S. Ct. at 454-55.)