That's your answer. Throw a dart into a crowd of democratic politicians (just make sure to throw it hard) and democrats across the board, and a good number of independents, will vote for whoever it hits because Donald Trump is still deeply unpopular.
The reason this is possible is because Biden has become toxic and has now outed himself as completely doddering, he's lost both the high and low information voters at this point so replacing him will only be a net benefit for Democrats. Wheel Klobachar or Bill de Blasio out there for all I care. People would quite literally vote for a Roomba. Are you understanding this? I'm telling you, explicitly, anyone stands a better chance over Biden.