There's no indication that Democratic delegates in large numbers would opt for another candidate to lead the party in November's election. But “Fox News Sunday” host Shannon Bream asked Lichtman what obligations Democratic delegates have “if President Biden says he’s not going to leave the ticket.”

Mr. Biden’s cleanup effort comes as a growing number of Democrats have called for him to step aside, the latest coming on Saturday from Representative Angie Craig, a House member from a swing district in Minnesota. A number of donors have also vowed to withhold money from his campaign until Mr. Biden passes the torch.

U.S. President Joe Biden has defiantly rejected calls that he step aside from the presidential race against Republican opponent Donald Trump, presenting a challenge to fellow Democrats who are concerned his age will dissuade voters.