What is the effect of counsel not presenting the defense of diminished mental capacity at trial?

Eckstrom contends he was denied effective assistance of counsel as a result of his trial counsel's failure to present the defense of diminished mental capacity. Eckstrom argues that such failure cannot be justified as a reasonable strategy decision. Specifically, Eckstrom asserts that his counsel's argument that the evidence was insufficient as a matter of law to sustain a first degree murder conviction under People v. Anderson, 70 Cal.2d 15, 447 P.2d 942 (1968), was inappropriate for his case. Eckstrom maintains that, at a minimum, his counsel should have raised the defense of diminished capacity as an alternative defense. Significantly, Eckstrom argues that there is a reasonable probability that the outcome of his trial would have been different if counsel had presented the defense of diminished capacity.