The best working theory that I've heard is that he wanted to be famous and carry out a mass shooting. He did extensive research on school shooters. He also researched the Democratic National Convention. He did searches on both Trump and Biden. Trump's event was closer.
"One emerging theory by investigators, based in part on the timing and subjects of his online searches, is that the shooter was looking to carry out a mass shooting and that the Trump event's proximity and timing offered the most ready opportunity, according to a US official briefed on the matter."
Investigators remain puzzled about possible motives for Saturday's attempted assassination of the former president, finding little to point to political or ideological intentions for the attack.
abc7.com
But this doesn't play into your imaginary 'he was proven to be left wing' dipshittery. So of course, you ignored it all, and folded it into your batshit conspiracy.
But why would I ignore that he was a registered republican, described by his classmates as a conservative, who debated conservative talking points with fellow students, who the FBI linked to extremist anti-immigrant rhetoric online?