Is evidence of mental disease, defect, or disorder admissible on the question of whether a defendant had the capacity to form the specific intent to commit the crime charged?

Evidence of mental disease, defect, or disorder is not admissible on the question of whether a defendant had "the capacity to form" the specific intent to commit the crime charged. ( 28, subd. (a).) While this evidence is admissible on the question of whether the defendant "actually formed" that intent (ibid.), whether the defendant did so is a question for the jury ( 29). Thus, an expert may not opine on the ultimate question of whether the defendant had the required mental state at the time he or she committed a crime. (Ibid.; see People v. Mills (2012) 55 Cal.4th 663, 672.)