There is no feeling of obligation to play fair and get along with the other guy even if his politics differ with yours.
I don't think it was so much the "his politics differ from yours". I think it was the "rape is a-okay with me!" that did it. I mean, the guy's clearly an idiot, nobody's arguing about that. He's lied about literally everything he promised to his voters, I think nobody's really debating that at this point. That's all fine, you believe a liar like that at your peril. If you're willing to buy his line, you're a fool and your folly is your privilege. But when he declares that half of human race is fair game for assault, I stop feeling any obligation to play fair and get along - the man's a scumbag, straight up.
(if that hadn't done it, the fact that he's got the Klan in his corner should really make you think twice about whether you want to make excuses for him - if you're a decent human being, you don't play nice with Nazis)