I disagree that Trump would be such a shoe-in for 2020. The Democrats just need a better candidate.

I think with the currently developing scandals (especially sexual assault allegations), and likely many more scandals between 2016 and 2020, they'd need someone even less liked than Hillary for him to have a shot.

The bigger threat is indeed whatever media empire he might try to launch after the election. (Scarily, I could picture him doing so whether he wins or loses.)