If someone voted for Trump and strongly regretted their choice, then I wouldn't consider them awful. I would consider them extremely dumb and/or misguided, though...

I would definitely stop seeing a friend or family member if they turned out to be fascist/racist. (Very unlikely scenario!) But if it had been a minor political disagreement (not on this level at all), then I wouldn't mind too much.

If someone I knew really fucked up royally (by voting for Trump or something disgusting like that) AND realized their mistake, then I usually believe in second chances. As a rule of thumb, because a few things in life are unforgivable imo. I would at least treat them with respect and behave in a nice way around them if they regretted their former political ways. I wouldn't want to be close with a person like that, NEVER, but some people actually change.