The Insanity Defense in the Court

It's entirely understandable, of course, that the lawblogs are focusing on today's Hamdan case.  Following Orin Kerr's lead, though, I thought I'd put in a plug for the Court's other decision, in Clark v. Arizona, in which Justice Souter, for six, refused to constitutionalize the M'Naghten rule and rejected a challenge to Arizona's "Mott rule," according to which evidence about a defendant's mental incapacity is admissible to establish the insanity defense, but not to negate the relevant statute's mens rea requirements.   Orin quotes an interesting passage:

[I]t is clear that no particular formulation has evolved into a baseline for due process, and that the insanity rule, like the conceptualization of criminal offenses, is substantially open to state choice. Indeed, the legitimacy of such choice is the more obvious when one considers the interplay of legal concepts of mental illness or deficiency required for an insanity defense, with the medical concepts of mental abnormality that influence the expert opinion testimony by psychologists and psychiatrists commonly introduced to support or contest insanity claims. For medical definitions devised to justify treatment, like legal ones devised to excuse from conventional criminal responsibility, are subject to flux and disagreement.  There being such fodder for reasonable debate about what the cognate legal and medical tests should be, due process imposes no single canonical formulation of legal insanity.

I was also intrigued by the Court's discussion of the interplay between the "presumption of innocence" and Arizona's "presumption of sanity," as well as by the discussion of the reasons supporting Arizona's rule.  Here's a bit:

Next, there is the potential of mental-disease evidence tomislead jurors (when they are the factfinders) through the power of this kind of evidence to suggest that a defendantsuffering from a recognized mental disease lacks cognitive,moral, volitional, or other capacity, when that may not bea sound conclusion at all. Even when a category of mentaldisease is broadly accepted and the assignment of a defendant’s behavior to that category is uncontroversial, theclassification may suggest something very significantabout a defendant’s capacity, when in fact the classification tells us little or nothing about the ability of the defendant to form mens rea or to exercise the cognitive, moral, or volitional capacities that define legal sanity.

I also note, with some distress, that Justice Souter used the phrase "fraught with considerable peril" (slip op. 36).  Similarly, Justice Thomas wrote, concurring in Monday's Beard case, that "judicial scrutiny of prison regulations is an endeavor fraught with peril."  Justice Kennedy is, I understand, the new center of power on the Court.  Still, I hope this Kennedy-esque "fraught with peril" stuff does not mark the beginning of a trend!  (See, e.g., Casey, 505 U.S. at 852 ("fraught with consequences for others")).