But as concerns have grown over Biden’s ability to do his job, with some polls placing her within striking distance of Trump in a hypothetical match-up, Republicans have racheted up their attacks.

As vice president, Harris would be an obvious candidate to replace Biden if he chooses to stand down - something he still insists he will not do - although other “new generation” alternatives have some also been named, such as California governor Gavin Newsom, Transport Secretary Pete Buttigieg and Michigan governor Gretchen Whitmer.

But trying to sidestep Harris would prove exceedingly difficult for the party, not least because it would spark a major backlash from sections of the black community, who Democrats need to show up in force on polling day.

“If you do something that infuriates her or alienates her, those voters may not show – and that’s a problem,” one Democrat strategist told this masthead.

Nonetheless, if named as the party nominee Harris would have the benefit of taking over money raised by the Biden campaign and inherit campaign infrastructure, the strategist said.

Loading

She also has the highest name recognition among all the alternatives, and the highest polling among other would-be contenders.

Party elders such as South Carolina Congressman Jim Clyburn - who helped Biden secure the presidential nomination by ensuring the black community rallied behind him in 2020 - said he would support a Harris candidacy if Biden stepped down.

But he added: “I want this ticket to continue to be Biden-Harris. And then we will see what happens after the next election.”

But others, such as former Ohio Democratic Congressman Tim Ryan said “we have to rip the band-aid off” and get behind Harris.

“@VP⁩ has significantly grown into her job, she will destroy Trump in debate, highlight choice issue, energize our base, bring back young voters and give us generational change. It’s time!” he wrote on X.

Amid the panic, White House press secretary Karine Jean-Pierre reiterated today that Biden had no plans to pull out of the race and shot down reports that he is weighing up his options as “absolutely false”.

And Harris - along with the other potential replacements - have continued to back the president publicly. Appearing outside a fund-raiser in San Francisco on Tuesday, the vice president said she was “proud to be Joe Biden’s running mate.”

“Look, Joe Biden is our nominee,” she also told CBS News. “We beat Trump once, and we’re going to beat him again. Period.”

Loading

The president and vice president also had lunch privately at the White House on Wednesday and made a surprise joint appearance on a call to Democratic National Committee staff, reiterating that they were in the fight together.

White House chief of staff Jeff Zients held a separate call with about 500 White House staff in which he admitted that the last few days had been challenging.

According to Jean-Pierre, he also “talked about the importance of coming together as a team and also having each other’s backs.”

The pep talk came as a new New York Times/Siena poll found Trump leading Biden by six percentage points among likely voters and nine points among registered voters nationwide - a three-point shift toward Mr. Trump since the last Times/Siena survey, which was taken immediately before the debate.

However, according to statistician Nate Silver, the poll showed the debate had not “completely upended public opinion about the candidates”, but rather exacerbated Biden’s political liabilities surrounding his age, “which had already imperiled his re-election chances.”

Get a note directly from our foreign correspondents on what’s making headlines around the world. Sign up for the weekly What in the World newsletter here.