I'm not American, but here's my 1€...
The trouble you have is neither keeping nor replacing Biden is clearly a better option. You've got two bad options, and I've no idea which is worse. Add on that bad actors (looking at you Russia!) are for sure trying to influence the election... who the fuck knows what the answer is.
I've been thinking about this all morning, and I think the bad actors are pushing both options simultaneously, the goal being to cause in fighting and apathy among Democrats. This is easily defeated though: pick an option ASAP - it doesn't matter which - and get 100% behind it.