Although restatements of professional conduct, such as ABA Guidelines, can be useful guides to whether an attorney’s conduct was reasonable, they are relevant only when they describe the professional norms prevailing at the time that the representation occurred. In this case, the lower court erred by applying 2003 ABA standards to a trial that occurred eighteen years earlier. Moreover, the lower court erred by treating the ABA Guidelines “as inexorable commands with which all capital defense counsel must comply.” Such standards are merely guides to what is reasonable; they do not define reasonableness. The Court went on to reject the defendant’s arguments that counsel was ineffective under prevailing norms; the defendant had argued that his lawyers began their mitigation investigation too late and that the scope of their mitigation investigation was unreasonable. The Court held that even if the defendant’s counsel had performed deficiently, the defendant suffered no prejudice.