Trump is never going to be impeached. In fact, I’m betting that in 2018 he is going to get a filibuster-proof senate and in 2020 win a second term in office. One in three Americans believe he can do no wrong.
History seems to show that when a President has low approval ratings, it often does not bode well for his party in Congress getting reelected.
Also, in 2020, he will likely not be running against Hillary Clinton. If Trump had run against Sanders, it would be a different story than running against her. And if you remember, he did not win the popular vote. Winning the electoral vote but not the popular vote is not that common. Plenty of people hated them both during the general election, but if the Democrats can find someone who is not despised equally as much as Trump then they have a decent shot at winning in 2020.