isn't that common? a lot of the people who killed or tried to kill American presidents weren't people who were super into politics or involved in large political organizations. The idiot who tried to kill Regan was in love with jodie foster.
iirc, it's only really true of the guy who tried to kill reagan.
Lincoln's assassin was pro-confederate.
Charles guiteau, who killed Garfield was insane, but he did it for political-adjacent insanity. He worked for a paper for a time and wrote pro-garfield articles, and thought Garfield owed him a government appointment as "thanks".
Oswald was involved with a lot of weird underground leftists, and was radicalized in the marines towards a pro-commie outlook.
The guy who threw a grenade at Bush did so out of hate for the US, and for the pro-US politician that was onstage with bush.
Crooks motive seems to be murky, but he did rant about different political activities online.
The other guy who tried to get Trump was 100% left leaning.
Basically only the guy who tried to get reagan was 100% apolitical nutso, followed by charles guiteau, who was politically motivated, but also insane and unreasonable to think he'd get a spoil's system reward for writing some articles.