WASHINGTON >> The Supreme Court ruled today that states can prevent criminal defendants from pleading insanity without violating their constitutional rights. The decision could prompt states across the country to toughen standards for defendants who wish to plead not guilty by reason of insanity.

The justices’ 6-3 decision came in a case from Kansas, where James Kraig Kahler was sentenced to death for killing his estranged wife, two teenage daughters and his wife’s grandmother.

Kahler wanted to mount an insanity defense, but Kansas is one of four states that eliminated a defendant’s ability to plead not guilty by reason of insanity. Idaho, Montana and Utah are the others. Alaska also limits the insanity defense.

Justice Elena Kagan wrote for the court that “Kansas takes account of mental health at both trial and sentencing. It has just not adopted the particular insanity defense Kahler would like. That choice is for Kansas to make — and, if it wishes, to remake and remake again as the future unfolds,” Kagan wrote in upholding a ruling from the Kansas Supreme Court.

Kagan’s three liberal colleagues dissented. Kansas “has eliminated the core of a defense that has existed for centuries: that the defendant, due to mental illness, lacked the mental capacity necessary for his conduct to be considered morally blameworthy,” Justice Stephen Breyer wrote for himself and Justices Ruth Bader Ginsburg and Sonia Sotomayor.