I still think Biden is a very strong chance to roll Donald, but if they concede that Biden isn't up for it and either he steps down pre-election or they reveal there is ANY chance he steps down mid term, he will not win the election.
Dems have to back Biden and go full steam ahead with him as their nominee and expect he serves a full term.
If they stick with that plan, they can beat the Republicans.
Anything else hands the Gop the presidency.