Trump won't finish out the first term. If he runs for a second term, he loses. Any other Republican who runs has a much better chance.
"Accidental Presidents" don't do well. See: John Q. Adams, Rutherford B. Hayes, and so on. Popular vote losers tend to be very unpopular by the end of their presidencies and since this is Donald Trump, I assume that he won't run for a second term having burned through his political capital by 2020. (I think he'll be impeached by 2019).
This is a pretty good read on the situation. Dubya only won reelection because of 9/11 and patriotism. Even then, he only squeaked out a 2.5% win. Clinton would have been a one-termer as well.
