Speculation has been rampant in the US about Joe Biden stepping down – either willingly or otherwise – as Democratic presidential candidate, following his disastrous debate performance.

The 81-year-old and his campaign have reportedly shrugged off concerns about his mental capacity to do the job of US president for a second term – and beat challenger Donald Trump.

But concerns remain at an all-time high following last week’s televised debate.

Despite Trump again indulging in a spree of unsubstantiated or false claims, many still considered him to be the winner on the night.

Biden’s performance, by contrast, was marked by stumbling over words and incoherent sentences.

His underwhelming show was criticised by the media, detractors and Democrats – setting fire to speculation he might be replaced as the candidate for November’s election.

David Axelrod, long-time adviser to former US president Barack Obama, told CNN “panic” had set in, and there would be “discussions” about whether Biden should continue.

Publicly, Biden has reaffirmed his commitment to seeking re-election, and senior Democrats continue to maintain he is the party’s best shot at keeping Trump out of the Oval Office.

But there is still wriggle room, because he will not be officially nominated as Democratic presidential candidate for some weeks.

Behind closed doors, Biden gathered his family at Camp David at the weekend – reportedly at least partly to discuss his political future – amid further rumours of serious concerns within the Democratic Party about his prospects.

If the party does decide Biden is too risky, here are five of the top candidates who could potentially replace him.

Photo: Getty

Kamala Harris

Vice-President Kamala Harris has been staunchly supportive of Biden whenever questioned over his competency, or  otherwise.

She could also potentially fill his shoes.

At 59, she is a relatively fresh face in a presidential candidacy pool filled with senior citizens, has no issues with public speaking, and is already a heartbeat away from presidency as second-in-command.

But the initial enthusiastic wave of popularity she rode into the position on has died down, with a recent Politico and Morning Consult poll revealing her approval ratings are almost in sync with Biden’s low results.

The poll showed only a third of voters think it’s likely Harris would win an election were she to become the Democratic nominee.

Some of this poor reception could be down to factors such as she is sometimes not seen as having done much to effect change while in office.

As she’s a woman of black and South Asian descent, sexism and racism might also be factors.

Photo: Getty

Gretchen Whitmer

Michigan Governor Gretchen Whitmer was co-chair of Biden’s 2020 presidential campaign and was on his shortlist for vice president.

She gained national attention in 2020 for a public back and forth with then-president Trump over Covid measures, and was subject to a kidnapping plot over her stance.

Whitmer has a strong supporter base in Michigan and a track record of significant progress on abortion access, gun law restrictions, and free universal preschool within the state.

Photo: Getty

Gavin Newsom

Under Governor Gavin Newsom, California has protected reproductive rights, expanded health care to undocumented immigrants, and enacted police reforms aimed at reducing rates of racial profiling and excessive force.

But California’s $US46 billion budget deficit, just a few years after it produced a surplus of more than $US100 billion, may put a significant dent in his popularity.

This has led to delays in promises such as pay rises for health care workers and child-care expense assistance in a state budget approved at the end of June.

Newsom also continued to publicly back Biden amid the fallout of last week’s debate, indicating he is not throwing his hat in the ring for presidential candidate just yet.

Photo: Getty

JB Pritzker

Illinois Governor JB Pritzker has continuously given Biden his full support during the current campaign, but some pundits feel he could also be a potential replacement.

If Pritzker was chosen, the election could become a battle of the billionaires; an heir to the Hyatt Hotel fortune, Pritzker also ran private equity firm Pritzker Group with his siblings until 2017.

As state governor, he has helped protect reproductive and LGBTQI+ rights, made it easier for victims of gun violence to sue gun makers, and has not minced his words when criticising Trump, labelling him a “selfish blowhard”.

Photo: X/@JoshShapiroPA

Josh Shapiro

Pennsylvania Governor Josh Shapiro has held his position for just 18 months, but his popularity in the US’s largest swing state is not something to be dismissed.

He also won the respect of some Republicans, with 42 per cent in Pennsylvania reporting positive perceptions about how he’s doing his job in his first term as governor.

But, like the other potential presidential candidates, Shapiro has voiced strong support for Biden and is more strongly considered a prospect for the 2028 presidential race.