re: Is there any realistic democratic candidate you could see defeating Trump in 2020?

Here's the deal, georgewest:

If the economy remains sound and in expansion mode, if unemployment remains at full employment levels, if the collapse of ISIS gets more media attention, if an infrastructure bill gets passed....I think he stands a very good chance of being reelected.

Incumbency tends to be an advantage.

I think if enough actual american factors like the economy remain positive, he has a very good chance of winning again.

There would be no good reason to vote him out besides dislike of tweeting.