Well people in this country were stupid enough to vote for the Tories, then stupid enough to vote for brexit, so why can't Trump win?
I have no idea why Hillary Clinton is so unpopular. Maybe politics is becoming more polarised over there as well. If so, then I suggest that we're all screwed.
I also don't know how much a Trump presidency would affect us, but I'm pretty sure it would affect America's credibility throughout the rest of the world, rather like Boris and brexit has affected hours.
So no, sorry, no useful answers there. I don't understand US politics at all.
Eta. It's becoming increasingly obvious that facts don't actually matter where political campaigning is concerned. Whoever can tell the most pandering lies and promise to create the most populist fantasy world will win.