Washington (CNN) The Supreme Court on Monday ruled against a Kansas man who argued his constitutional rights were violated when the state refused to allow him to bring an insanity defense.

In a 6-3 opinion, the Court said an insanity defense that considers whether a defendant can distinguish between right and wrong is not constitutionally required.

Under the law in Kansas, a defendant can argue mental illness only to prove that he did not intend to commit the crime. Otherwise, mental illness cannot be used as a defense. Four other states have also abolished an insanity defense.

The ruling could inspire other states to do so and will make it more difficult for the mentally ill to defend themselves.

"Today's decision leaves much, if not most, of the scope of insanity defenses to individual states," said Steve Vladeck, CNN Supreme Court analyst and professor at the University of Texas School of Law.

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