The Dems capture Congress and move to impeach.... Once Trump is enmeshed in the impeachment process how can he possibly run for re-election? Of course he can legally do it, but practically he cannot.
Remember Clinton. Impeachment made him way more popular as many people felt there as an overreach. I wasn’t one of them but his popularity went way up after the House impeached him.
If the Dems impeach Trump, I think you would see the same thing.