Kahler v. Kansas: Can States Abolish the Insanity Defense?

In Kahler v. Kansas, decided in 2020, the Supreme Court ruled 6-3 that the Due Process Clause does not require a state to offer an insanity defense based on the defendant’s inability to tell right from wrong. Justice Elena Kagan’s majority opinion upheld a Kansas statute that lets defendants use mental-health evidence only to show they could not form the intent the crime requires.¹ The decision leaves each state free to draw its own line between mental illness and criminal responsibility.

What Kansas Law Actually Allows

Kansas replaced the traditional insanity defense with what is often called the mens rea approach. Under K.S.A. § 21-5209, mental disease or defect is a defense only if it prevented the defendant from forming the mental state the charged crime requires. The statute closes the door on anything more: “Mental disease or defect is not otherwise a defense.”²

In practice, a Kansas defendant can still argue that psychosis kept him from understanding he was pulling a trigger, or that he was aiming at a human being. What he cannot argue is that he knew exactly what he was doing but, because of delusions, believed it was morally justified. The traditional not-guilty-by-reason-of-insanity verdict is gone from the trial phase.

That is a real narrowing. Under the M’Naghten rule that most states follow, a person in a psychotic break who kills someone he believes is a demon can be acquitted because he did not understand his act was wrong. Under the Kansas approach, that same person can be convicted if the evidence shows he intended to kill the person in front of him, whatever delusion drove the intent.

How the Case Reached the Supreme Court

James Kahler’s marriage began to unravel in 2008, and by 2009 he was heading toward divorce, growing estranged from his children, and struggling with severe depression and obsessive-compulsive disorder. He was seeing mental-health professionals and had been prescribed antidepressants, anti-anxiety medications, and sleep aids, but was not taking them as directed.³

In November 2009, Kahler went to his wife’s grandmother’s house, where his family had gathered, and shot and killed his wife, his two daughters, and the grandmother. Charged with capital murder, he tried to argue at trial that his mental illness left him unable to understand his actions were morally wrong. Kansas law did not permit that argument as a route to acquittal. The jury convicted him and imposed the death penalty.³

Kahler appealed, arguing the Constitution guarantees every defendant the right to raise a full insanity defense. The Kansas Supreme Court disagreed, and the U.S. Supreme Court took the case on the question of whether due process requires states to recognize a moral-capacity test.

The Majority’s Reasoning

Justice Kagan framed the question narrowly: does due process require a state to adopt an insanity test that turns on the defendant’s ability to recognize that his crime was morally wrong? The Court asked whether the moral-incapacity rule is “so rooted in the traditions and conscience of our people as to be ranked as fundamental,” and concluded it is not.¹

The historical record, the majority found, was too mixed to support that claim. Early common-law writers focused on whether a defendant could form criminal intent at all, not on moral awareness. The moral-incapacity prong gained independent footing only with the English M’Naghten case in 1843, and American states have continued experimenting since, including with tests based on volitional incapacity, the inability to control one’s behavior. Because no single formulation had become universal, none could be constitutionally required.¹

The majority also stressed that Kansas had not shut mentally ill defendants out entirely. Psychiatric evidence can still negate the required mental state at trial, and defendants can present mental-health evidence at sentencing to argue for reduced punishment or placement in a psychiatric facility rather than prison. Those pathways, the Court held, meant Kansas’s framework was not fundamentally unfair.¹

What the Court Did Not Decide

Kahler also asked the Court to rule that the Eighth Amendment’s ban on cruel and unusual punishment independently requires a moral-incapacity defense. Because he had not raised that argument in the Kansas courts, the Supreme Court declined to address it.³ That question remains open for a future case. The due-process holding does not foreclose it.

Justice Breyer’s Dissent

Justice Breyer, joined by Justices Ginsburg and Sotomayor, argued that Kansas’s statute strips away the heart of a defense that has existed for centuries. His core claim was that criminal punishment has always required moral blameworthiness, and that a defendant whose mental illness destroys his capacity for moral judgment cannot fairly be found guilty, whatever his technical intent to perform the physical act.³

Tracing seven hundred years of Anglo-American law, Breyer concluded that while the words used to describe the insanity defense have shifted, they all express the same idea: a person so mentally impaired that he cannot be held morally responsible should not be convicted. Kansas’s approach, he wrote, “requires conviction of a broad swath of defendants who are obviously insane and would be adjudged not guilty under any traditional form of the defense.”³

Breyer also rejected the argument that shifting mental-health considerations to sentencing is an adequate substitute. A lighter sentence for someone who should never have been convicted, in his view, is not a constitutional remedy.

How Mental Illness Still Enters a Kansas Case

Even after Kahler, mental illness has not disappeared from Kansas criminal proceedings. It operates in two other places.

At sentencing, K.S.A. § 21-6815 lets judges depart from the presumptive guidelines sentence for “substantial and compelling reasons.” Mental impairment is specifically listed as a mitigating factor: the court may consider whether the defendant, because of physical or mental impairment, “lacked substantial capacity for judgment when the offense was committed.”⁴ The factor is permissive, not mandatory. A judge can reduce the sentence or direct placement in a mental-health facility rather than a standard prison, but is not required to do either.

Competency to stand trial is a separate protection that Kahler did not touch. Under K.S.A. § 22-3303, a defendant found incompetent is committed for evaluation and treatment, on an outpatient or inpatient basis, at an appropriate state, county, or private facility, and the trial does not proceed until competency is restored.⁵ Competency and criminal responsibility answer different questions at different times, though. A defendant can be lucid during trial while having been deeply psychotic during the crime, and being competent to sit in a courtroom says nothing about moral responsibility for conduct months or years earlier.

Which States the Ruling Protects

Kansas is one of four states that have eliminated the traditional affirmative insanity defense. Idaho, Montana, and Utah follow similar mens-rea-only approaches, allowing psychiatric evidence solely to challenge whether the defendant formed the mental state the charged crime requires.⁶ The other states all offer some form of insanity defense, though the specific tests vary.

One difference sets Kansas apart from the other three. Idaho, Montana, and Utah each provide a “guilty but mentally ill” verdict, which allows the court to direct psychiatric treatment during incarceration. Kansas does not offer that alternative at the conviction stage; it handles mental illness exclusively through the sentencing-departure framework.⁴

Kahler shielded all four state frameworks from due-process challenges. Before the ruling, there was a live question about whether the Constitution required some version of the moral-incapacity test. Under the Due Process Clause, that question is now settled. The Eighth Amendment argument the Court set aside could resurface, but for now the states retain broad authority to define the relationship between mental illness and criminal responsibility.

1
Supreme Court of the United States. Kahler v. Kansas
2
Kansas State Legislature. Kansas Code 21-5209 – Defense of Lack of Mental State
3
Justia. Kahler v. Kansas, 589 U.S. ___ (2020)
4
Kansas Office of Revisor of Statutes. Kansas Code 21-6815 – Imposition of Presumptive Sentence; Departure Sentencing; Mitigating and Aggravating Factors
5
Kansas Office of Revisor of Statutes. Kansas Code 22-3303 – Commitment of Incompetent Defendant
6
Connecticut General Assembly. Office of Legislative Research – Abolishment of Insanity Defense