Does a failure to introduce mitigating evidence at the penalty phase constitute ineffective assistance of counsel?

In People v. Durham (1969) 70 Cal.2d 171, 191-192, 74 Cal.Rptr. 262, 449 P.2d 198 we rejected the argument that the failure to introduce mitigating evidence at the penalty phase constituted ineffective assistance of counsel. We reached this conclusion based on the "totality of the circumstances," especially in view of defendant's failure to point to any significant evidence in mitigation, the fact that counsel presented a well-reasoned closing argument and fully cross-examined prosecution witnesses, and counsel's concern that the scope of cross-examination would lead to damaging testimony.