How could Democrats replace President Joe Biden as the party's nominee?

Unless President Joe Biden removes himself from the 2024 presidential race, it's essentially impossible for any other candidate to earn the Democratic nomination, according to party rules. And even if he does leave, it would be challenging to confirm a replacement.

Following Biden's debate performance on Thursday, a groundswell of panic from political observers -- including from some Democrats -- triggered discussion over the possibility of replacing Biden at the top of the party's ticket in November.

Biden -- who has maintained he plans to remain in the race -- is set to soon be formally nominated as the Democratic presidential nominee. Biden will be nominated at a virtual convention between the dates of July 21 and Aug. 7, party members decided during a vote last month -- a move that rectifies a conflict over election deadlines in Ohio, which complicated the president's ballot access in that state. It also puts the virtual convention before the party's Aug. 19 in-person convention.

If Biden remains in the race, there is only one real option for forcibly ousting him as the nominee at this stage: for more than 1,976 out of the more than 3,894 individuals who have already selected to be Biden's pledged delegates to refrain from voting on for him on the first ballot during the Democratic National Committee's virtual nomination. Then, there would be a sort of "brokered convention" with the involvement of unpledged delegates on additional rounds of balloting.

But there are several reasons why this scenario would be far-fetched, including the will of delegates and the technicalities of several party rules.

Longtime members of the party who have worked closely on writing rules changes in the past tell ABC News that they have been actively discussing how it would work to change rules should the nominee need to be replaced, however. And some DNC and state party members have argued that a delegate selection of the nominee, in the event of an open convention, would be hugely undemocratic because voters would not be involved in the process at this stage.

If Biden remains in the race

Most of Biden's delegates, which were finalized at the completion of delegate selection on June 22, were chosen on a state-by-state basis as top supporters of the president and are unlikely to shift their backing, according to conversations between ABC News and national and state party leaders, along with seven individual delegates.

"That's not even remotely a topic of conversation," said Aaron Sims, a Biden delegate in Nevada, said of changing his vote from Biden.

"We were a little bit worried about [his debate], but we think that so far, he's run a really great campaign. You know, we're four months away from the election, and the idea of changing -- shifting to someone brand new that we have to introduce to the country, it would just be so much of a cluster that I don't think it's doable. I think ... we would actually be forfeiting the election if we did that," Sims added.

There is still technically a chance that any of these delegates could change their minds, however.

"I am still supporting President Biden until this moment," Sami Khaldi, a Biden delegate from Michigan, told ABC News.

But Khaldi added that he was "definitely monitoring the situation very closely."

"If he will do much better on the campaign trail, we see that he's still a strong candidate, I'll support him. Otherwise, we will have a different discussion later on with the rest of the Democratic Party."

Unlike Republican delegates, Democratic delegates are "pledged" rather than "bound" to a candidate, and party rules say that delegates "shall in all good conscience" reflect the views of those who elected them. There is no official penalty if a delegate votes differently.

The party could vote during one of their upcoming committee meetings to create some sort of penalty for pledged delegates who don't support Biden. But as of now, there will be no punishment.

If a Biden delegate sits out of the first round of balloting instead of backing the president, their vote would simply not count.

But if that delegate supports another candidate -- or even backs former candidate Dean Phillips, who earned three delegates from Ohio, or Jason Palmer, who earned three delegates from American Samoa, their votes would just be counted as "present."

This is because Biden is the sole candidate who is officially eligible for nomination at this stage, according to the party, which cites party rules that will be formalized on Aug. 19.

One of the rules requires that a presidential candidate has "established substantial support for their nomination," and has a proven track record as a Democrat who is faithful to the interests of the party. The rule states that the candidate must publicly affirm -- in writing -- that they are a Democrat, which comes with any of the other necessary eligibility requirements on a state level. That written affirmation needs to have been accepted by the DNC's Rules and Bylaws Committee, too.

Another rule echoes that sentiment, along with requiring the candidate must be registered to vote and that they were registered during the last election. It also means the candidate should be a bona fide Democrat "as determined by the National Chairperson" of the DNC.

The temporary rules also state that each nomination request must be accompanied by a petition including between 300 and 600 delegate signatures, not more than 50 of which may come from one delegation. A delegate may not sign more than one petition -- over 99% of delegates are pledged already to Biden so they would be unable to nominate another candidate.

If there were more "present" votes than Biden votes, the opportunity for a "brokered" convention arises (though virtually, as voting will take place). This would happen because Biden would be unable to secure the majority of the pledged delegates on the first ballot.

But the party would be at a loss for who they would be able to replace him, as no other candidate is eligible for nomination at this time.

Again, thousands of these pledged delegates would have to revolt in order to make any sort of impact on Biden's nomination.

"I don't anticipate there being a real groundswell of opposition at the convention. I mean, he has 99% of the pledged delegates. It would take, you know, thousands of delegates all converging and opposing him at once, against the sitting president of the United States," election law expert Derek Muller, a professor at Notre Dame, told ABC News.

And because Biden's nomination will occur even earlier now (ahead of the party's in-person convention beginning on Aug. 19) -- and virtually -- Muller said the likelihood of any real opposition is even smaller.

"To the extent they're doing that even earlier and continue to adhere to that process, I think it's just deeply unlikely that it would result in anyone except Biden. Again, I think it really would take him voluntarily stepping down, for most -- for any of these serious scenarios to play out realistically," Muller said.

If Biden drops out

On the off-chance that Biden drops out of the race ahead of the nomination -- without a rule change -- many delegates who were assigned to Biden would likely go into the Democratic convention uncommitted, according to Elaine Kamarck, a senior fellow at the Brookings Institution and member of the DNC.

These delegates would not automatically shift to Vice President Kamala Harris. The presidential and vice presidential ballots are separate at the Democratic convention.

Individual delegates would suddenly have a lot of influence on whom their party nominates.

Harris -- as Biden's running mate -- would be a natural, even likely, destination for many Democratic delegates if Biden does leave the race.

Lara Brown, a political scientist and author of "Jockeying for the American Presidency: The Political Opportunism of Aspirants," told ABC News in January that she does not believe that the Democratic convention would be all that contested in the event Biden passed away. There could be a symbolic first ballot vote for Biden, "then essentially, [the convention could] create a point of order … and then do a second ballot," likely for Harris to be the nominee, Brown said.

But there remains the possibility of other options, including high-profile governors as well as members of Congress or Biden's cabinet.

An unclear variable still exists here, however, as no other candidate other than Biden is officially eligible for nomination without a party rule change.

ABC News' MaryAlice Parks and Oren Oppenheim contributed to this report.