I've made bad predictions all last year, but here we go.
If Trump lasts until 2019, he'll finish out his term. His own party is more likely to remove him than the Democrats. An unpopular President is bad for a party's brand. Trump is either crazy or crooked. If Mike Pence decides it's the former, the Vice-President can ask the Cabinet to vote to remove Trump under the 25th Amendment. If Paul Ryan decides it's the latter, then Congress can impeach.
The GOP has been trying to get rid of Trump for about two years now. President Trump will supply Republicans with plenty of pretext for removing him. They just need the will and the courage to act.
Democrats on the other hand, dread Mike Pence more than they hate Trump. Pence is the fiscal conservative that other Republicans pretend to be. As a member of Congress, he voted against the bank bailout twice. Pence will want to kill a lot of federal programs. And Pence is a much more disiplined candidate than Trump. Pence is not the man that Democrats want on top of the GOP ticket in 2020.