It's not too late for Dems to choose another candidate. Here's how it would work.

Biden's debate performance has led to mounting pressure for the Democrats to replace him. US politics experts explain how that could work.

• Biden's debate performance has led to mounting pressure for him to bow out of the presidential race.
• Experts said it's not too late, but a decision to drop out could lead to chaos, like in 1968.
• Biden could say he's not running, resign as president, or face delegate defections.

Can the Democrats replace President Joe Biden at the top of the ticket?

Following the president's fumbled debate performance on Thursday, this question could be on many people's minds.

And as Business Insider has previously written, history can usually guide us on what could happen.

In 1968, when President Lyndon B. Johnson dropped out of the race, his vice president, Hubert Humphrey, entered the Democratic primary, but he was too late to get on some states' ballots.

Humphrey amassed a larger share of delegates than his rivals, Robert F. Kennedy and Eugene McCarthy, but did not have the majority needed for the nomination.

This led to a contested Democratic National Convention in Chicago, marked by violent protests.

The nation, already facing upheaval with the Vietnam War and the assassination of Martin Luther King Jr., had been thrown into shock and mourning when Kennedy, the younger brother of late President John F. Kennedy, was assassinated in Los Angeles.

Delegates eventually voted to name Humphrey the nominee, but he ultimately lost the election to former Vice President Richard Nixon.

Biden may choose not to stand, but it could lead to chaos

If Biden were to drop out of the race before August, when Democrats are scheduled to formally nominate a candidate in Chicago, there would likely be another contested convention.

Mitch Robertson, a lecturer in US modern political history at University College London, told BI that such a scenario would evoke the tumultuous events of 1968 — a comparison that he said was both apt and disheartening.

Robertson said that, like 1968, which was precipitated by Johnson announcing that he wouldn't run for president, Biden would need to make the decision to decline his party's nomination.

Like Johnson, he could also pledge to serve the rest of his term in office.

Still, it would kick off a contest to find his replacement, as there is no formal mechanism for Biden to automatically anoint his successor.

Robertson said that the process could be bad news for the Democrats.

"The lessons of 1968 and the convention of 1968 in particular have always loomed large in the Democratic mind and the US political history mind as an unmitigated disaster," he said.

In 1968, it led to chaos and an election loss, which Robertson said would be the Democrats' main fears of a contested convention, "that it would do the same thing all over again."

It takes a majority of the roughly 4,000 pledged delegates to win the party's nomination. In the primaries and caucuses, Biden won 3,900 delegates.

Thomas Gift, director of UCL's Center on US Politics, explained that if Biden bows out, and the DNC rules don't change, his pledged delegates would become uncommitted, potentially leading to lobbying and voting for a replacement.

"I think that is still quite unlikely, but it is more likely than it was before last night," he told BI.

Gift said a key challenge is that there is "no obvious heir apparent."

Typically, the vice president is the go-to individual, but Gift said Vice President Kamala Harris's approval ratings are too low for her to be a serious contender.

"I think a lot of individuals would want to throw their hat into the ring," he said. "I think it would have the potential to create a lot of disorder, chaos, and conflict within the party."

Mark Shanahan, an associate professor at the University of Surrey, whose research focuses on US presidential politics, said the "best bet" is that Biden throws his support behind a strong new candidate before the August convention.

Governors Gavin Newsom and Gretchen Whitmer, as well as Secretary of Transportation Pete Buttigieg, are seen as potential candidates.

Shanahan continued: "The worst-case scenario for the Democrats is there's no clear succession by the time of the convention, which becomes, in effect, an 'open convention' and who takes on Trump in November is decided through a divisive faction floor fight in Chicago."

Biden could resign, but Harris wouldn't automatically become the nominee

Biden could go one step further. Under intense pressure, he could resign as president.

It would make Harris the president, but not necessarily the nominee.

"Even if Kamala Harris is president, it still doesn't mean that Biden can say, 'All my delegates are now hers,'" Iwan Morgan, emeritus professor of US History at UCL's Institute of the Americas, told BI.

"The rules are very clear," he said. "You're committed to a particular person on the first ballot."

The delegates wouldn't automatically transfer to Harris, so she would still need to win a majority of delegates at the convention, which Morgan said would involve a lot of "horse-trading" and intense lobbying.

Delegates could defect

Another scenario, which the experts said is pretty unlikely, is that delegates could defect en masse.

"Unchartered waters doesn't even begin to describe it," Morgan said. "Yes, they could do that, but it would need to be coordinated."

While delegates aren't legally bound to their candidates, they are largely presumed to be loyal.

The current DNC rules read that "delegates elected to the national convention pledged to a presidential candidate shall in all good conscience reflect the sentiments of those who elected them."

Theoretically, this provides some wiggle room, but not much.

"The point is the DNC is under Biden's control," he said. "It's just a question of what kind of influence can be brought to bear on Biden."

It's not too late, but it wouldn't be easy

Morgan said the Democrats still have time because the election campaign "proper" doesn't typically start until Labor Day in September.

However, he added that for a smooth process, "the sooner they can move Biden, the more chance they have to prepare for the convention."

John Owens, a professor of US government and faculty fellow at the American University's Center for Congressional and Presidential Studies, told BI via email that "given Biden's insistence on this early debate, there may be enough time for Democrats to turn this round."

But he said it's going to be a tall order and will depend on the flexibility of the party, as well as state rules and regulations making this possible.

Owens said one thing is clear to him: "Biden is toast, and if the Dems do not turn this around, US democratic procedures and culture may also be toast."