After two weeks, 42% of Americans want Trump impeached
Not only that but bookies in England are now offering even odds that he will be impeached or will resign before the end of his term.
Ladbroke's is giving him only a 4-1 chance of remaining in office longer than six months. Personally, I think he's probably safe for that long and quite a bit longer.
But given his personal instability, impulsiveness, and long-standing pattern of playing fast and loose with the law (he was already in violation of the Emoluments Clause of the Constitution the moment he took the oath), I would be very surprised if Mike Pence were not the Republican nominee for the White House in 2020.
Which is not by any means to say that he would win in November.