I would guess that democratic primary isn't even going to happen, I get that there could be some people who could run a campaign and all, but to be a nominee when the sitting president is a candidate would be a big trouble for anyone who wants to run.

I get it, Biden is not looking good for even some democrats, but no sitting president who ran for reelection lost the nomination as far as I can ever remember, hell until Trump most people who were presidents ended up running for a second term, bush had one, Clinton had one (cut short) bush Jr had one, and Obama had one, they all went for reelection and not just got the nomination, but won the election as well. So it would be quite difficult for anyone if Biden runs again.