Whether a death row inmate is precluded from establishing prejudice from his trial counsel's deficient performance during the penalty phase if his counsel did present some mitigating evidence at his capital trial

QUESTION PRESENTED On advice of counsel, Mr. Mashburn pleaded guilty to five counts of capital murder for killing his grandmother and her husband, a tragic crime for which Mr. Mashburn has never denied responsibility. The only question in this case has always been whether Mr. Mashburn should receive the death penalty. At trial, counsel cobbled together a last minute slate of witnesses, including two experts hired a month before trial, and failed to present compelling mitigating evidence of untreated mental illness and Mr. Mashburn’s state of mind at the time of the offense. Although lower courts agreed that counsel had performed deficiently, the Eleventh Circuit affirmed the summary dismissal of Mr. Mashburn’s habeas corpus petition, finding that Mr. Mashburn failed to show that he was prejudiced by trial counsel’s deficient performance. This Court has held that with respect to the “prejudice” prong of a Sixth Amendment ineffective assistance of counsel claim under Sétrickland v. Washington, 466 U.S. 668 (1984), a “probing and fact-specific analysis” of both evidence adduced at trial and in the habeas proceeding “applies . . . regardless of how much or how little mitigation evidence was presented during the initial penalty phase.” Sears v. Upton, 516 U.S. 945, 955-56 (2010) (per curiam). The question presented here is: Whether, under Strickland v. Washington, a death row inmate is precluded from establishing prejudice from his trial counsel’s deficient performance during the penalty phase if his counsel did present some mitigating evidence at his capital trial? i