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. 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 8:00pm (0000 GMT Saturday).