Democrat presidential candidate US President Joe Biden listens as Republican presidential candidate and former US President Donald Trump speaks during their debate in Atlanta, Georgia, US, Thursday. (Reuters)

After President Joe Biden's shaky performance at the debate with former President Donald Trump on Thursday night, some Democrats openly questioned whether he should be replaced as their candidate for the 2024 election.

There is a process for doing so, but it would be messy.

For answers on how that would work, Reuters spoke to Elaine Kamarck, a senior fellow at the Brookings Institution think tank, a Democratic National Committee member, and author of the book "Primary Politics" about the presidential nominating process.

This explainer is based largely on interviews with her.

What options do democrats have?

The Democratic Party has had no real Plan B for Biden as its presidential candidate. He ran virtually unopposed for the party's presidential nomination this year.

He will not be nominated officially until later this summer, so there is still time to make a change and a handful of scenarios to enact one: Biden could decide himself to step aside before he is nominated; he could be challenged by others who try to win over the delegates he has accrued; or he could withdraw after the Democratic convention in Chicago in August, leaving the Democratic National Committee to elect someone to run against Trump in his place.

So what happens next?

Right now, the process largely depends on Biden. He would have to agree to step down or face a challenger this late in the process who would try to force him to do so. So far Biden has shown no indications of wanting to step aside and no opponents have challenged him directly.

In fact some of his top potential replacements -- Vice President Kamala Harris and California Gov. Gavin Newsom -- spoke passionately in his defense after the debate, serving in a surrogate role that showcased their support but also contrasted their smooth delivery with his haltering one on the Atlanta debate stage.

What happens if Biden steps down?

Biden has spent the last several months accruing nearly 4,000 Democratic delegates by winning primary elections in US states and territories.

Those delegates would normally vote for him, but the rules do not bind or force them to do so; delegates can vote with their conscience, which means they could throw their vote to someone else.

If Biden "releases" his delegates by stepping aside, there could be a competition among other Democratic candidates to become the nominee.

Who would replace Biden?

Several candidates could step into the fray, but there is no obvious number one.

Vice President Harris would almost certainly be at the top of the list, but she has had her own problems after a rocky start in the job and poor polling numbers. The US Constitution dictates that the vice president becomes president if the president dies or becomes incapacitated, but it does not weigh in on an inter-party process for choosing a nominee.

How would a nominee be chosen?

There would likely be a free-for-all of sorts between the Democratic heavyweights vying for the job.

Candidates would have to get signatures from 600 convention delegates to be nominated. There are expected to be some 4,672 delegates in 2024, including 3,933 pledged delegates and 739 automatic or superdelegates, according to Ballotpedia.

If no one gets a majority of the delegates, then there would be a "brokered convention" in which the delegates act as free agents and negotiate with the party leadership to come up with a nominee.

What happens if Biden steps down after the convention?

If Biden steps down after the August convention, the 435 members of the Democratic National Committee would choose a new candidate. The members would meet in a special session to select a nominee.

Who are these 435 DNC members?

They are divided equally between men and women as well as various constituency groups including labor leaders, LGBTQ representatives, and racial minorities. Of the total, 75 are appointed at-large by the chair, while the rest are elected in their respective states.

Who could nominate an alternative in that case?

To nominate a candidate to replace Biden on the ballot, that person would have to have the support of a minimum number of DNC members -- perhaps around 60, though the exact number would be determined by the DNC's rules committee, which would lay out the rules for the proceedings before they started.

How would those votes be counted?

The DNC would likely hold its meeting in Washington and the votes would be counted there. Ballots would be coded, signed and collected by hand. If a vote were to happen very close to Election Day on Nov. 5, when it was not possible to meet in person, then it would likely be virtual. (Reuters)