United States President Joe Biden’s withdrawal from the 2024 presidential race has left Democrats grappling with unanswered questions about the way forward, with less than four months before election day.

Biden stepped aside on Sunday after weeks of pressure from fellow Democrats following a disastrous debate performance against former President Donald Trump in June.

Now, Democrats need to coalesce around a new nominee and re-energise their base if they want to defeat Trump,  analysts say. Vice President Kamala Harris is an early favourite to replace Biden, especially after she received the president’s endorsement. Biden also encouraged donors to contribute to Harris for her campaign.

Still, Biden’s decision to withdraw is not merely unusual — it is unprecedented in modern US politics. “We’re in uncharted territory here,” said Kyle Kondik, the managing editor for the Sabato’s Crystal Ball, a newsletter about elections published by the University of Virginia Center for Politics.

And Harris could face challengers seeking the Democratic nomination in the coming days.

The new nominee will be chosen at the Democratic National Convention in Chicago next month, when more than 4,000 party officials and activists, known as delegates, gather to vote.

There have been instances where parties have chosen their candidates in competitive conventions after the primaries. In fact, that happened frequently before the modern primary system was put in place in 1972, granting voters a greater say in the process.

But the Democrats’ current situation is different.

Having won nearly all pledged delegates,  Biden is now the first presumptive nominee of a major party to quit the race after the primaries have concluded.

The president ran in the primaries without any serious challengers and Democratic officials stressed early on that Biden – as the incumbent – will be the likely nominee.

“I don’t really think there’s any good recent precedent for it. Half a century or more ago, it wasn’t uncommon to go into the convention not necessarily knowing for sure who the nominee was going to be,” Kondik, who spoke to Al Jazeera earlier this week, said.  “But since then, we haven’t had this sort of situation where somebody dominates the primary season – but then steps aside later, in advance of the convention.”

With no historical precedent to follow, Democrats will have to improvise within their guidelines on how to choose their new nominee, analysts say.

While the change comes with risks, a new candidate could galvanise Democratic voters who had previously resigned themselves to the uphill battle of taking on Trump at a time when his lead over Biden had widened across battleground states.

Before dropping out, Biden was set to face Republican nominee Trump for the second presidential election in a row.

Meena Bose, a professor of political science at Hofstra University, said that while it is risky to change candidates so close to the elections, a shake-up at the top of the Democratic ticket could boost the party’s chances.  “A late change is not ideal but may bring more optimism than no change at all or, at the very least, might potentially be helpful down the ballot, if not in the presidential race,” Bose said.

Soon after Biden announced his departure from the race, he endorsed Vice President Kamala Harris to replace him at the top of the Democratic Party ticket.

Kondik said Biden’s endorsement makes a big difference. The president has the support of the overwhelming majority of delegates. And while they are not bound to back Harris, Biden’s backing could tip the scales in her favour. In the hours that followed Biden’s announcement, a flood of leading Democrats publicly endorsed Harris – from Senator Elizabeth Warren and state leaders of the Democratic Party to governors who were seen as potential rivals for the nomination, such as California’s Gavin Newsom and Pennsylvania’s Josh Shapiro.

The vice president also has national name recognition and can inherit the Biden-Harris campaign infrastructure.

Kondik said that nominating Harris was the “path of least resistance” for Democrats. Bose echoed that assessment, saying that Harris was the most “logical choice” to ensure a seamless transition. There is not a lot of time for an open competition for delegate support,” she told Al Jazeera.

Hans Noel, a professor at Georgetown University’s Department of Government, also said on Friday – before Biden’s announcement – that Harris was projected to take over the nomination.  “The vice presidential candidate does not automatically become the presidential candidate, but I think a lot of voters would sort of expect that,” Noel told Al Jazeera in an email.  “Given that she’s in that position, there are a lot of reasons not to go to someone else. She does have a lot of support in the party, but more importantly, nominating someone else would look like skipping over a Black woman, which would not look good for many in the party.”

The rules for the Democratic National Committee state that delegates can propose a new party nominee if they obtain the signatures of 300 fellow delegates, along with a signature of confirmation from the proposed candidate. But the party will, in all likelihood, coalesce around Harris to present a united front.

The Democratic Party now faces the anxiety-inducing question of how voters will respond to Biden’s departure from the presidential race, a considerable shake-up so close to the election.

US presidential campaigns require massive investments of cash and manpower to reach people across the country. Some start as early as two years in advance. Launching a campaign from scratch will not be easy.

“Campaigns take huge amounts of infrastructure, money and messaging to get through to the voters that we know are most undecided,” said Casey Burgat, the director of the legislative affairs programme at George Washington University.

Burgat explained that reaching undecided voters is also labour-intensive: “You need to hit them several times. You need to have people knocking on doors. There’s just a huge infrastructure to be built.”

What happens to the campaign funds Biden amassed is also a source of uncertainty. With no precedent for the current situation, questions have swirled over the fate of Biden’s war chest.

In the US, after all, election spending can run into millions, if not billions, of dollars.

But Burgat noted that campaign finance restrictions are less of an issue for Harris since she is already on the ticket as Biden’s vice president and has been part of his fundraising efforts.

However, if Biden’s exit has drawbacks, it also presents opportunities. Many voters had been unenthused about the prospect of an election between Biden and Trump.

Before Biden’s announcement, a recent poll from The Associated Press and the NORC Center for Public Affairs Research found that 65 percent of Democrats believed he should exit the race.

Just three in 10 expressed confidence that he had the mental acuity necessary to serve effectively as president.

Burgat says that a new, younger candidate could have an energising effect and give the party a much-needed boost. “The most common thing we’ve heard is: ‘I can’t believe these are our two options.’ People have been wondering how, in this country of 350 million people, their choice has been reduced to these two very unpopular candidates,” he said.