What happens if Biden steps out of the race?

President Joe Biden is vowing to stay in the election race even as some within the Democratic party are calling for him to step aside.  

While the commander-in-chief contends he is the Democrats' best chance to defeat Donald Trump, some within the party have speculated about possibly nominating another candidate.

Several media outlets reported Thursday that Rep. Nancy Pelosi, D-Calif., the former Speaker of the House, had a second phone conversation with Biden to insist that polling shows he cannot win against Trump, per CNN. 

RELATED: Biden’s COVID diagnosis comes amid renewed calls for him to step aside

A day earlier, California Rep. Adam Schiff became the highest profile Democrat to call for Biden to drop his reelection campaign amid the party’s plans for a virtual vote to formally make Biden its nominee in the first week of August. 

Who decides on the nominee?

Democrats replacing Biden as their nominee for president may be highly unlikely for a few reasons. The Associated Press notes that every state held its presidential primary already, binding their delegates to the primaries’ winner – in each case, Joe Biden. 

Democratic Party rules require that those delegates support him at the party's upcoming national convention unless he tells them he is leaving the race.

RELATED: Democrats on Biden's future: Two-thirds prefer a new nominee, poll shows

According to the AP, the conventions and their rules are controlled by the political parties. The Democratic National Committee could meet before the convention opens on Aug. 19 and change how things will work, but that isn't likely as long as the president wants to continue his push for another White House bid. 

The Democratic National Committee could change these rules before the convention, but it’s unlikely if Biden continues his reelection campaign.

It is important to note that Kamala Harris, despite being Biden's running mate, cannot automatically assume the top of the ticket if Biden steps down. Biden cannot simply decree that she replace him.

RELATED: List of top Democrats who have called on Biden to exit race

LiveNOW from FOX spoke with an expert about who could decide on the Democratic nominees for president. John Hanley, an associate lecturer at the School of Politics, Security and International Affairs at the University of Central Florida, explained how things could unfold.  

"Well, I think, you know, the Democrats are running out of time, to have anything that would resemble a normal process. They have their convention in the middle of next month, in August," Hanley said. "What I think you'd have to see is some sort of coordination between the major figures in the party – people like Barack Obama, Nancy Pelosi, Hakeem Jeffries, Biden himself – to choose someone who would be acceptable to the various wings of the party and who would be the standard bearer for the party. 

"Historically, parties would go into their conventions and choose the nominee largely at the conventions, if you go back 100 years or so. But, given the time that's available and the likelihood of about 4,000 Democratic convention goers deciding on a nominee, I think that's unlikely."

Who could be the nominee?

Vice President Kamala Harris

Kamala Harris is the most likely successor, given her role as vice president and her extensive political background, including her tenure as a U.S. Senator and California's Attorney General. Despite her historic achievements, she faces challenges due to her polling numbers and previous presidential campaign performance.

California Governor Gavin Newsom

Gavin Newsom, the governor of California, is seen as a strong candidate due to his progressive policies and national visibility. His handling of the COVID-19 pandemic and recent policy initiatives have kept him in the national spotlight.

Michigan Governor Gretchen Whitmer

Gretchen Whitmer has gained national attention for her handling of the COVID-19 crisis and her strong stance on issues like reproductive rights and infrastructure. Her leadership in a key swing state adds to her appeal as a potential candidate.

Secretary of Transportation Pete Buttigieg

Pete Buttigieg, the former mayor of South Bend, Indiana, and current secretary of transportation, remains a notable figure within the Democratic Party. His successful 2020 presidential campaign and his work in the Biden administration position him as a potential candidate.

Illinois Governor J.B. Pritzker

J.B. Pritzker, the governor of Illinois, has been a prominent advocate for progressive policies on healthcare, labor rights, and climate change. His leadership and substantial personal wealth could make him a formidable candidate.

New Jersey Senator Cory Booker

Cory Booker, a U.S. senator from New Jersey, has consistently been a strong voice on criminal justice reform, economic equality, and healthcare. His experience and national recognition could help him rally support within the party.

Minnesota Senator Amy Klobuchar

Amy Klobuchar's moderate stance and strong performance in the 2020 Democratic primaries have kept her in the conversation as a potential candidate. Her focus on bipartisan solutions and effective governance could appeal to a broad spectrum of voters.

Where do the campaign contributions go?

The president has amassed a lot of campaign contributions for his reelection bid. But if he decided to drop out of the race, Vice President Kamala Harris could have access to the money in their campaign account if she were to replace Biden as the Democratic presidential nominee. 

Although Biden has not indicated that he’s dropping out of the race, Time reports that some Democrats said they would endorse Harris if Biden decided to exit the race primarily because she would inherit the campaign cash – which is more than $90 million – since her name is already on the current presidential ticket.

The vice president's name is on filings for Biden’s statement of candidacy and his campaign account’s statement of organization, allowing her to use the money if she continues with the Biden presidential campaign, NBC News reports.

Citing a political expert, Time reported that campaign fundraising could get "complicated" with a different Democratic presidential nominee because most of the cash in the Biden-Harris campaign account would be refunded to donors if the nominee was another candidate. 

The Associated Press contributed to this report.  This story was reported from Washington, D.C.