The left wing has given Trump an enormous amount of material to use in ads. I see no way that Trump does not get re-elected if he decides to run. Middle America loves him and thanks to the growing number of red-states (OH, PA, MI, WI, IA), he will have the electoral advantage with room to grow it more.
If he caves on amnesty, he won't be re-elected. I'd still vote him because the alternative is the likes of Mrs. Bill Clinton, but millions will just stay home (what's the use?).