In terms of replacing Biden I think that would be the worst scenario for the democrats themselves. After pumping up the propaganda about defending democracy and making that their central issue, even just the suggestion of replacing Biden, especially with someone that neither ran in the primary nor was voted for pretty much takes their biggest selling point right off the table Yet at the same time now they see Biden is incredibly weak and they can't keep gaslighting the public into trying to prop him up as a strong leader and try to make them ignore about how most of America generally has suffered under their whole regime the past 4 years. Kamala is the only reasonable replacement for Biden since she is technically part of the ticket and also is the VP, but yet at the same time this is a huge complication since really Kamala is even more unpopular than Biden. They're just in a position where there is no good answers for them. The best course of action for them is to try to end the party infighting before the convention and fall in line behind Biden it seems.