I think would have to be someone who was not vetted and rejected in the primaries. It could have been Cumao, but he unequivocally declined. Notice that Bernie, Lizze and Zero didn’t give their half-hearted tepid endorsements of Slow Joe until after Cumao made it clear he would not be the nominee. They were holding out hope that he would agree to sub for Joe. When he didn’t they capitulated and endorsed.
I don’t see anyone out there who didn’t run in the primary who could step in. Neither did Lizzie, Bernie and Zero. They are mailing it in with Slow Joe. The only one who doesn’t know that is Joe.
I’ve said from the beginning that no one in the Primary will be the eventual nominee
Even if they stick with Joe, and God forbid, he should actually win, it’s my understanding that they can replace him any time before Dec 14, when the electors meet