Via Stephen Fowler:

…20-year-old shooter at #Trump's rally.

Voter registration shows Thomas Crooks was a currently registered Republican who also donated $15 through ActBlue, the Democratic-allied organization, in 2021.
Former President Donald Trump is rushed offstage during a rally in Butler, Pa.

it is SUPER important to note that there's nothing about ideology/motive/etc. that's known or released at this time, and each one of those data points are not indicative of anything by themselves