IF the Dems take the House this fall, I can see them having an impeachment vote on Trump, but would every democrat vote for it? It's easy to say "Hell yeah, impeach the bastard" when you're in a deep blue district, but not so cut and dried when you're out there in a purple or red district that could go against you in a heartbeat. I'd say if they did have that vote, then win or lose the house would wing back to the GOP in 2020. And there would be a good chance Trump would win re-election too, all other things being equal.
As far as the Senate goes, not a chance in hell. There's no way the dems are going to get 67 seats in the Senate, and no repub is going to vote against Trump. It may be that Trump will resign for health reasons first, which is possible I guess but at this point unknown and unlikely. Right now, it looks like Trump will still be our President in 2020, and the way things are going with the economy, he's going to win re-election for another 4 years.