The premise of this entire thread is a bit unrealistic.

Biden will be the nominee. No one credible is running against him in the primary. The reason no one credible is running against him in the primary is because none of them could beat him in a primary.

This may seem counter-intuitive. After all, so many Democrats would prefer a different candidate! But the problem is, those Democrats don't all prefer the same different candidate. They don't even prefer the same type of candidate. Some want Joe Biden, but younger; some want a more progressive candidate; some want a candidate that has a different foreign policy; some want someone with different demographics.

You can't beat someone with no one. The "generic opponent" is never on the ballot. When confronted with any candidate, most people can imagine some theoretical alternative that's more the perfect candidate for them - but when looking at a ballot with Newsome, Harris, Buttigieg, Klobluchar, Booker, Michelle Obama, or whomever else might be that theoretical candidate, none of the real world candidates is likely to do better than Biden in a primary. The "I'd prefer someone else" candidate has no negatives, no compromises, no positions on issues where there are divisions of opinion within the party. Real candidates have all those things.

And that's even before, you know, actual campaigning. Biden isn't out there spending time or resources trying to convince Democrats to support him in a primary, because there is no primary (effectively). Since he's not making the case to the base, so to speak, he's going to look especially vulnerable among Democrats. But if anyone really entered the race to fight him (like, say, a Newsome) and the campaign machinery kicked up, they'd never have a prayer.

Yeah - so Biden will be the nominee (barring the usual caveats that he might get hit by a bus or have a heart attack or something).