With Biden Out, What Happens Next? Here’s What We Know.

Now that President Biden has ended his re-election bid, Democrats must choose a replacement nominee in less than a month, condensing what is typically a yearlong primary campaign into just a couple weeks.

Here are answers to six key questions as Democrats navigate a possible post-Biden future.

Mr. Biden endorsed Vice President Kamala Harris, but the official selection of a nominee will be made by the more than 4,600 Democratic National Convention delegates, a body of senior party figures, local activists and elected officials who were selected at state party conventions this spring. Most were vetted by the Biden campaign.

Those delegates, who typically serve a functionary role, will now preside over a decision of historic import. Never in the modern history of American politics has a candidate who swept through a party’s presidential primaries abandoned his campaign so close to a national convention. There is no precedent or historical record to consult, and the party’s rules are not always clear on the details of what will unfold next.

That would be difficult to do logistically.

Only officials at the Democratic National Committee and the Biden campaign have the full roster of delegates. If someone decided to run against Ms. Harris, the first challenge would be to gain access to the people who will make that decision.

Without access to the delegate list, alternative candidates to Ms. Harris are effectively blocked from both canvassing the delegates for their opinions and trying to persuade them to support someone other than Ms. Harris. There is no evidence to date that any serious political campaign other than Mr. Biden’s and the D.N.C. has made an effort to reach out to the convention’s delegates.

They are free agents, able to