You make a good point about cause and effect. I would simply add that while Trump may be the effect of an already degrading political discourse, he has certainly only served to worsen it still.
Yes, there was already partisan bickering, blaming, shaming, and name-calling. But there wasn’t — so far as I can remember — the kind of sexism, racism, calls for violence, and provocation garnering this much attention. Not in America. It’s the kind of thing we hear from some far-right Euro-skeptic parties, like Golden Dawn, but not from a serious candidate of an established political party in the United States.