concurring in the judgment:
I concur in the judgment. I stress that the State, in the appeal, did not contest the district court’s determination that trial counsel performed deficiently at sentencing. So, the first element (the performance element) of Strickland was never put into controversy in this appeal. I also stress that I doubt — and do not understand today's opinion to say — that the failure to introduce evidence of mild or borderline mental retardation in a capital sentencing proceeding will be, or almost always will be, or even usually will be enough to satisfy the prejudice element of Strickland. We need to be cautious about applying what is said in the context of Eighth Amendment opinions in the materially different context of deciding ineffective-assistance-of-counsel cases.