Washington (AFP) - With his reelection bid on the line, US President Joe Biden sits down Friday for a crucial TV interview to persuade doubters of his physical and mental fitness for a second White House term.

The one-to-one with the ABC network has been hyped as the most consequential of the 81-year old’s long career, after a disastrous campaign debate with Donald Trump triggered panic within his Democratic Party and calls for him to pull out of the race.

The Biden campaign has pushed back hard on any suggestion he may withdraw, and just hours before the ABC interview it released an aggressive campaign travel schedule for the rest of July.

At least three of his party members in Congress have called on him to step aside, as have several major newspaper editorial boards and a raft of Democratic-supporting political commentators.

The president has said that he is “not leaving” and is “in this race to the end,” but post-debate polls have shown Trump’s lead widening.

Biden has also not yet spoken publicly without a teleprompter since the debate, other than some brief remarks.

Friday’s interview with ABC presenter George Stephanopoulos, set to be recorded during a campaign trip to Wisconsin, will be a key moment for Biden to try to dispel the worries and reset expectations.

With soaring anticipation for the interview, ABC has switched up its original plan of airing excerpts through the weekend, and will instead broadcast it in full Friday at 8:00 pm (0000 GMT Saturday).

Biden will face an experienced interviewer known for his firm, effective style.

Stephanopoulos worked for former Democratic president Bill Clinton during his first campaign and was one of his closest advisors during his first term in the White House.

- Campaign schedule -

Biden will have to win back confidence with a clear and cohesive performance after he was often incoherent in the debate.

A growing number of Americans have called for him to prove he has the energy to defeat Trump in November, and handle another four years in the White House.

Former House speaker Nancy Pelosi, one of the most influential Democratic voices, has deemed it “essential” that the president do more major interviews.

Other supporters have called for a long-form news conference to judge his stamina.

The White House has announced that he will hold a press event during the NATO summit in Washington next week, but has not revealed any details on its format or length.

Biden’s travel plans include Pennsylvania this weekend, then the NATO meeting, and back on the campaign trail with a swing through the southwest United States.

The president will “engage in frequent off-the-cuff moments over the course of the month, as he has consistently throughout this campaign,” his team said, seeking to emphasize his folksy charm.

The election is “a choice between Joe Biden – a fighter for American families – and Donald Trump – a convicted criminal,” it added.

Trump has meanwhile dared Biden to another debate, or an “all-on discussion,” saying that he was ready “anytime, anywhere, any place.”

With speculation still swirling over a potential switch-up at the top of the Democratic ticket, Kamala Harris, the nation’s first female vice president, has suddenly been in the spotlight.

The 59-year-old former California prosecutor – who joined Biden at Thursday’s July 4 celebrations – has been performing a delicate balancing act since the debate.

She has offered unwavering support for Biden in public but is standing by as a leading contender to replace him if he steps aside.