Whether the Fourteenth Amendment's Due Process Clause requires Kansas to provide an insanity defense that acquits a defendant who, because of mental illness, could not understand that his intentional criminal act was morally wrong.
Holding
No. Due process does not require a State to adopt a moral-incapacity, right-from-wrong insanity defense.
Reasoning
A state rule defining criminal liability violates due process only when it offends a principle of justice so deeply rooted in the Nation's traditions and conscience as to be fundamental. Historical practice is the primary guide, and this demanding standard ordinarily leaves States broad authority to define criminal offenses and defenses.
The Court's precedents had already rejected the idea that due process constitutionalizes a particular insanity test. In Leland v. Oregon, the Court held that a State could use a moral-incapacity test rather than an irresistible-impulse test. In Clark v. Arizona, the Court upheld Arizona's choice to retain moral incapacity while excluding cognitive incapacity as an independent insanity defense. Those cases establish that no single formulation of legal insanity is the constitutional baseline.
Kansas has not eliminated every insanity defense. Its statute allows a defendant to use mental-disease evidence to show an inability to form the mens rea required for the crime. Thus, a defendant who did not understand the nature and quality of his actions—for example, one who did not comprehend that firing a gun would kill a person—may be acquitted because he lacked the required intent.
Kansas also permits defendants to introduce a wide range of mental-health evidence at sentencing. A defendant may argue that mental illness prevented him from appreciating moral or legal wrongfulness, or from controlling his conduct, in support of reduced punishment or commitment instead of imprisonment. Kansas therefore channels some mental-illness evidence to sentencing rather than excluding it altogether.
The historical record did recognize a broad principle that insanity can excuse criminal conduct, but it did not establish moral incapacity as the exclusive or indispensable definition of insanity. Early common-law sources and decisions used varying formulations, including tests focused on the defendant's capacity to understand his actions, possess reason, or form felonious intent.
M'Naghten's Case later articulated a two-pronged rule: a defendant could be excused either for not understanding the nature and quality of the act or for not knowing that the act was wrong. Although that formulation became influential, the States continued to adopt divergent approaches, including irresistible-impulse, product-of-mental-illness, cognitive-capacity, and legal-wrongfulness tests.
The distinction between moral wrongfulness and legal wrongfulness is consequential. A defendant may know that killing is illegal while, because of a delusion, believing the killing morally required by God. A State using legal wrongfulness may convict that defendant, while a State using moral wrongfulness may acquit. This persistent variation further undermines the claim that the moral-incapacity rule is a settled constitutional minimum.
Rules about insanity reflect contested medical judgments and competing views about free will, blameworthiness, public safety, and the purposes of punishment. Because those judgments remain subject to uncertainty and revision, the Constitution leaves States substantial room to experiment. Kansas could reasonably decide that a person who intentionally kills is not wholly blameless even if mental illness led the person to believe the killing was morally justified.