Could Democrats replace Biden as their nominee? Here's how it could happen, and why it's unlikely

As President Joe Biden attempts to reassure supporters following his widely panned debate performance on Thursday, Democrats still worried about having him at the top of the ticket in November have few realistic options at their disposal, at least as far as party rules and historical precedent are concerned.

Those fretting over Biden as the Democratic nominee have some alternative, albeit unlikely, scenarios to consider: One involves Biden stepping aside voluntarily, the other, and by far the least likely, involves an 11th-hour effort to defeat him at the convention by winning over pledged delegates he has won in the nominations contests, who are technically obligated to support him only by “good conscience” in the party’s rules.

Challenges to the presumptive nominee can occur, but there are significant hurdles, according to Elaine Kamarck, a senior fellow at the Brookings Institution and an expert in the party's nominating process.

“It has been tried, and it usually fails,” said Kamarck, who is a longtime member of the Democratic National Committee's Rules and Bylaws Committee.