A large proportion of Trump supporters are not for Donald Trump the human being and all the things he's done. They're for the Republican party being in power; they're against Clinton for her faults (real or imagined); they're for someone who isn't a mainstream candidate being in charge for once. There's all kinds of reasons to support the GOP Presidential candidate that many people may see as more important than the insane, racist, sexist things Trump has said and done.
(I say this as a left-leaning guy by Canadian standards. Believe me, I'm terrified you guys might actually elect that monster.)