The re-election campaign for President Biden says it has raised a whopping $27 million since his rocky debate performance against former President Trump.

From the day of the debate through Friday evening, the Biden-Harris campaign told Fox News that it had raised $27 million.

The updated figure comes after the campaign said on Friday that it raised $14 million in "a sign of strength of our grassroots support" on debate day and the morning after.

The campaign also noted Friday that 11 p.m. to 12 p.m. on Thursday – the first hour after the debate – was the single best hour of fundraising since the campaign's launch in April 2023.

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The large sums of cash come as Biden's campaign seeks to address Democratic Party panic over whether he is mentally fit to serve as president following his disastrous faceoff with Trump in Atlanta, Georgia, on Thursday.

"I know I’m not a young man, to state the obvious," Biden, who at 81 is the oldest president in the nation's history, told cheering supporters at a Friday afternoon rally in the crucial battleground state of North Carolina.

"Folks, I don’t walk as easy as I used to. I don’t speak as smoothly as I used to. I don’t debate as well as I used to," Biden acknowledged. "But I know what I do know. I know how to tell the truth. I know right from wrong. And I know how to do this job. I know how to get things done. And I know, like millions of Americans know, when you get knocked down you get back up."

The president, pointing to his 2024 rematch with Trump, emphasized, "I would not be running again if I did not believe with all my heart and soul that I can do this job."

Struggling with a raspy voice and delivering rambling answers, Biden struggled during portions of the debate. Several political analysts noted, however, that the president sharpened his answers as the debate progressed.

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Biden's uneven and, at times, halting performance grabbed the vast majority of headlines from the debate and sparked a new round of calls from political pundits, publications and some Democrats for the president to step aside as the party's standard-bearer.

Top Biden allies have pushed back against such talk as they defended the president and targeted Trump for "lying" throughout the debate.

Two Democratic sources confirmed to Fox News that top Biden campaign officials worked to calm concerns and fears as they huddled privately on Friday at a previously scheduled meeting with top party donors.

"Biden‘s record grassroots fundraising from the day of the debate is critical. It helps blunt the criticism from Biden’s performance," veteran political strategist and Democratic National Committee member Maria Cardona told Fox News.

Cardona, a top Biden supporter, said spotlighting the fundraising "reminds Democrats that there is enthusiasm for the president and urgency to make sure that the liar and criminal Donald Trump doesn’t get close to the Oval Office."

Another Democratic strategist and presidential campaign veteran said that team Biden's focus on fundraising "is their best and maybe their only card to play."

Trump campaign senior adviser Brian Hughes discounted the Biden fundraising.

"As of last week, the Biden campaign has spent $100 million on cable, TV and radio. They've spent money on a bloated organization. Yet President Trump's lead has grown in battleground states, and now we see polling and enthusiasm on the ground putting Virginia and Minnesota in play for the GOP nominee for the first time in many election cycles," Hughes told Fox News.

The Trump campaign – enjoying the post-debate narrative – had no need to immediately emphasize its own fundraising, but told Fox News Friday afternoon it brought in $8 million the day of the debate.

A major conservative activist group is preparing for legal battles in case the Democratic Party chooses to pull President Biden out of the running before or after he becomes the nominee.

The Heritage Foundation, one of the United States' most prominent and well-connected conservative activist groups, is laying the groundwork in case a sudden switch-up in the Democratic roster sparks a legal war.

"We are monitoring the calls from across the country for President Biden to step aside, either now or before the election, and have concluded that the process for substitution and withdrawal is very complicated," Executive Director of The Heritage Foundation’s Oversight Project Mike Howell said in a statement. "We will remain vigilant that appropriate election integrity procedures are followed."

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Heritage has already identified multiple states in which a switch away from Biden before or after the nomination could mean serious trouble for the Democratic Party.

In a separate statement, the Oversight Project warned, "If the Biden family decides that President Biden will not run for re-election, the mechanisms for replacing him on ballots vary by state. There is the potential for pre-election litigation in some states that would make the process difficult and perhaps unsuccessful. 

"Given the expected intensity of election integrity concerns in this election cycle, policymakers and the public should be educated and aware of the contentious path ahead," it added.

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Heritage points out that many states — including swing states such as Georgia, Nevada and Wisconsin — might not allow a replacement on the ballot

Wisconsin does not allow a candidate's name to be withdrawn from the ballot except due to death. 

Nevada allows changes to its ballot up until 5:00pm on the fourth Friday of June in the election year. It also allows special consideration for if nominees die or are determined to be mentally unable to proceed. 

Georgia would allow Biden to withdraw up to 60 days before the election. If Biden withdraws afterward, his name would remain on the ballot but votes for him would be discarded.

Other states have restrictions on timing and the reason for withdrawal from ballots, while others have no procedures on the books, making the prospect of switching Biden out a minefield.