Lets say he loses Congressional majorities in November in some Blue Tsunami, fails to get re-elected in 2020, or he resigns, is impeached, or has to leave the White House for medical reasons. Hell, lets assume the best case scenario–the nation undergoes a complete political conversion, and the Conservatives are effectively purged from the body politic altogether.
Regardless of what happens, we will still be living in a country where about one quarter or one third of the adult population will feel that not only do they live in a tyranny dedicated to their destruction, but that their last chance of redemption and freedom has been frustrated and discredited by a conspiracy of traitors. Trump will not be a disgraced thug and buffoon to them, he will become a martyred saint. And all the economic, religious, cultural and racial divisions we brought into the new millennium will still be with us–and getting deeper every day.
The nation will be faced with a militant and extremist faction that sees itself as a culturally and racially homogenous, patriotic, entitled majority surrounded and besieged by rabble, a foreign and subversive minority led by an unscrupulous over-educated elite. Those people will have guns, they’ve been dying for an excuse to use them, and will feel they have every moral justification to do so.