To the point of the OP, I think the game plan is to ride the super-prog wave. Put in a strong younger progressive black woman as VP to help counter all the complaints against Uncle Joe (old, moderate, racist, misogynist), prop him up through the elections and as far as he'll go before they have to invoke the 25th, then go for 8 more years with the fresh blood VP. They get to either take credit for Joe's official 4 years if they go well, or blame him if it goes south. Side benefit is that the VP may inspire enough of the base (a la Obamamania '10) to pull off a sweep of both Houses in '22.