If someone is truly insane (highly unlikely here), jurors will reject the defense, opting for Guilty but Mentally Ill, which covers a broad array of mental illnesses, yet secures the conviction and life sentence, whether served in prison or a lock down state facility for crazy people.
This asshole is toast. But, he signed up to be toast.
From a very conservative Republican family. “Firearms are King” kind of family.
He will quickly learn that he ain’t all that tough.