In terms of replacing Biden ahead of the election, this is pretty much not possible, both the democrats and republicans are deluding themselves to think this will happen. Many of the swing states have already had their deadline pass for who will appear on the ballot, and so if they replace Biden with someone like Michelle Obama then their votes just won't count in several key battleground states and by default they'll lose the election that way guaranteed. Even just the fact they are discussing this is a very bad look for them after all the effort they made about casting themselves as the defenders of democracy. I mean you have to seriously think about this for a moment, they made their central platform that they are the defenders of democracy and yet here they are talking about appointing people that didn't even run in the primary elections. Those who have been under the spell of the bewitchment of democrats now that they have had the illusion shattered can do one of two things; they can stay with their own lies and hatred that makes them loyal to those that misled them and dig their hole deeper or they can surrender their ego and take the outstretched hand of Trump and together we can make America great again.