What would happen if Biden drops out of the election?

The matchup against former President Donald Trump underscored one of Biden’s greatest vulnerabilities—his age—but Biden has so far vowed to stay in the race.

One day after the first Democratic member of Congress—Texas Rep. Lloyd Doggett—called on Biden to end his re-election bid, other lawmakers were raising concerns about the fallout of the president continuing to be the Democratic nominee.

“Too much is at stake to risk a Trump victory," Doggett said.

Some of Biden’s top donors, meanwhile, have latched on to a “Star Wars" analogy aimed at keeping nervous supporters from defecting, The Wall Street Journal reported: Biden is like Yoda—old and frail yet wise and influential—whereas Trump is like Jabba the Hutt, a gluttonous and powerful gangster.

If Biden were to exit from the race, the process to replace him wouldn’t be easy.

What happens if Biden drops out?

All of the Biden delegates preparing to go to the Democratic National Convention in Chicago would become uncommitted delegates.

The Biden delegates slated to support him in August were approved by the campaign, meaning they are likely loyal to the president. This could make them more likely to cast their vote for whichever candidate Biden supports upon stepping down.

Democrats announced in May that they planned to nominate Biden before the convention through a virtual roll call vote, but they haven’t set a date. If Biden does drop out and the party throws its support behind a new contender, the Democrats could nominate a new candidate before they gather in Chicago.

What about Kamala Harris?

Harris doesn’t automatically become the nominee just because she is vice president—the delegates have already been selected, so she is on the same footing as any other person. Still, her status and connections in the party make her the likeliest replacement. An endorsement from Biden wouldn’t bind delegates to Harris, but it would likely help her rally support.

Anyone else?

The Democratic Party has a host of political stars, including California Gov. Gavin Newsom, Illinois Gov. J.B. Pritzker, Michigan Gov. Gretchen Whitmer and Transportation Secretary Pete Buttigieg. All have been vocal supporters of Biden’s campaign.

What if Biden drops out after the convention?

Once the convention ends, for the Democrats to choose a new candidate, Democratic Party Chair Jaime Harrison would need to consult with Democratic governors and members of Congress before filling the vacancy.

What would happen to the Biden campaign’s funds?

The Biden-Harris campaign has raised a considerable amount of money toward his re-election, and campaign-finance experts say that cash can’t simply be transferred to another candidate if Biden drops out—unless that candidate is Harris, who would just inherit the campaign committee. Were Harris to assume the top of the ticket, funds donated toward the Biden-Harris campaign would be at her disposal since she and Biden were running together.

Should Harris succeed Biden, “she would maintain access to all the funds in the committee and could use them to advance her presidential candidacy," said Shanna Ports, senior legal counsel at the Campaign Legal Center.

What about pro-Biden super PACs?

Super PACs can accept unlimited amounts of money from donors, who can give millions at a time, unlike a campaign, which faces individual donor limits. Election law prohibits direct coordination between super PACs and campaigns, and super PACs wouldn’t be directly affected if Biden ends his campaign. There are several super PACs supporting Biden’s re-election bid, preeminently a group named Future Forward, as well as others such as Unite the Country.

This explanatory article may be periodically updated.

Write to Owen Tucker-Smith at Owen.Tucker-Smith@wsj.com and Sabrina Siddiqui at sabrina.siddiqui@wsj.com