U.S. President Joe Biden, fighting to save his endangered re-election effort Friday, defiantly declared that "I'm staying in the race" during a campaign rally in a critical battleground state as he prepares to sit down for a network television interview where his every answer is sure to be scrutinized for evidence of his competency and fitness to run for office.

In front of roughly 300 supporters at a Wisconsin middle school, Biden again acknowledged his subpar debate last week, saying he "can't say it was my best performance." Amid speculation over what he would do, he had an answer: "I am running, and I'm going to win again."

"I beat Donald Trump," Biden said. "I will beat him again."

Biden, relying on a Teleprompter for his remarks, attacked his presumptive Republican challenger almost immediately, laying into Trump by pointing out that the former president once said that "George Washington's army won the revolution by taking control of the airports from the British."

As the crowd laughed, Biden continued, "Talk about me misspeaking."

The rally preceded an interview that could be a watershed moment for Biden, who is under pressure to bow out of the campaign after his disastrous debate performance against the 78-year-old Trump ignited concern that the 81-year-old Democrat is not up for the job for another four years.

The interview with ABC's George Stephanopoulos, being taped after the campaign rally in Madison, Wis., is expected to be intensive and probing, and two people familiar with the president's efforts said he had been preparing aggressively. They spoke on condition of anonymity to discuss internal planning.

There was broad agreement that Biden cannot afford to have another "bad day," which is how he wrote off his debate flop. It was not clear that even a so-so performance would be enough to satisfy concerns about his fitness to serve.

'Millions' will see interview: White House

The White House itself was raising the stakes for Biden's interview, with press secretary Karine Jean-Pierre saying that "millions of Americans" were expected to watch.

While private angst among Democratic lawmakers, donors and strategists is running deep after Biden's damaging debate performance, most in the party have held public fire as they wait to see if the president can restore some confidence with his weekend travel schedule and his handling of the Stephanopoulos interview. It will air in full on ABC on Friday night.

But at least three House Democrats have called for Biden to step down as the nominee, with Rep. Seth Moulton, a Democrat from Massachussets, expressing his concerns in a Thursday radio interview and joining Reps. Lloyd Doggett and Raúl Grijalva, Democrats from Texas and Arizona respectively, in seeking an alternative.

"President Biden has done enormous service to our country, but now is the time for him to follow in one of our founding father, George Washington's footsteps and step aside to let new leaders rise up and run against Donald Trump," Moulton told the radio station WBUR on Thursday.

• With Joe Biden and Justin Trudeau both facing calls to step aside, Cross Country Checkup wants to know: When did you decide it was time to step down from a job or something important to you? Fill out this form and you could appear on the show or have your comment read on air this Sunday.

While not going that far, Massachusetts Gov. Maura Healey said in a carefully worded statement Friday that Biden now has a decision to make on "the best way forward."

"Over the coming days, I urge him to listen to the American people and carefully evaluate whether he remains our best hope to defeat Donald Trump," Healey said. "Whatever President Biden decides, I am committed to doing everything in my power to defeat Donald Trump."

Meanwhile, Sen. Mark Warner reached out to fellow senators earlier this week to discuss whether to ask Biden to exit the race, according to two people familiar with the effort who requested anonymity to talk about private conversations. The Virginia Democrat's moves are notable given his role as chair of the U.S. Senate Intelligence Committee and his reputation as a lawmaker who has supported Biden and developed working relationships with colleagues in both parties. Warner's effort was first reported by The Washington Post.

There were also a few signs of discontent at Biden's campaign rally on Friday, with one supporter on stage waving a sign that read "Pass the torch Joe" as the president walked onto the stage. His motorcade was also greeted at the middle school by a few people urging him to move on.

Many Democrat lawmakers split

Many Democratic lawmakers, who are hearing from constituents at home during the holiday week, are split on whether Biden should stay or go. Lawmakers have been deeply frustrated by his campaign's response to the crisis. Privately, discussions among the House Democrats flared this week as word spread that some of them were drafting public letters suggesting the president should quit the race.

WATCH | Biden intent on staying in the race: 

Defiant Biden stays in the race: ‘No one’s pushing me out’

Despite mounting pressure to step down after a dismal debate performance, Joe Biden will ‘absolutely not’ abandon the U.S. presidential race, the White House has announced. Biden reportedly told staffers, ‘I am running…. No one’s pushing me out.’

Yet pushback from other House Democrats was fierce, and none of the letters from either Democrats in competitive re-election bids or those in easier races that were reportedly being discussed were ever made public. 

"Any 'leader' signing a letter calling for President Biden to drop out needs to get their priorities straight and stop undermining this incredible actual leader who has delivered real results for our country," said Rep. Frederica Wilson, a Democrat from Florida, who is an influential member of the Congressional Black Caucus.

Biden appears to have pulled his family and inner circle closer while attempting to prove that he's still the Democrats' best option for competing in November's election.

The ubiquitous presence of Hunter Biden in the West Wing since the debate has become an uncomfortable dynamic for many staffers, according to two Democrats close to the White House who requested anonymity to discuss the sensitive matter.

For many staffers, the sight of Hunter Biden, just weeks after his conviction on felony gun charges, taking a larger role in advising his father has been unsettling and a questionable choice for the high-stakes moment, they said.

Biden's re-election campaign is pushing ahead with aggressive plans despite the uncertainty. It plans to pair his in-person events with a fresh $50-million US ad campaign this month meant to capitalize on high viewership moments like the Summer Olympics that begin in Paris on July 26.