Barring a Civil-War-inciting act, Trump is going to win in 2020, and the Dems know it. The question is not who will be on the top of the ticket, but who will be the VP candidate. My guess is that it will be Tulsi Gabbard, and she will be groomed for 2024 as the communist-who-looks-like-a-moderate, which is how the Dems won in 1992 and 2008.
Some are thinking she could pass as a RINO and grab some R support.