The sad honest truth is probably that there are more bigoted people out there that won’t vote for a Dem if it isn’t a white guy than people who would add votes to one who isn’t, particularly in swing states. Maybe I’m too cynical…

As for replacements, even the people who some polls show as being slightly more popular than Biden haven’t been through anywhere near as much of a dedicated smear campaign as he has, and if they were, we don’t know how they’d poll.