...for the Democratic nominee. Clandestinely, of course.
Leak a poll showing Trump a bare 1 point ahead after the debate and brag that he is CRUSHING Biden. Complain that Biden is the most liberal American president in American history.
Now they're piling on in ways that increases the likelihood of his exit. They will end up regretting this. The best-case scenario is a diminished Biden remaining, rather than a Gretchen Whitmer or Josh Shapiro replacing him.
After all, he's far more likely to lose, but if he wins, there will be massive buyer's remorse almost immediately. He'll decline even further in office and do massive damage to the Democrats.
If Biden wins, nothing changes from the current situation except Trump will have 'lost' twice and may get barred from trying again. Biden or Harris alone won't necessarily bring down the party as a whole.