Struggling Biden faces big test with TV interview

US President Joe Biden, scrambling to defuse a political crisis over his shaky debate performance, will take part in a television interview that will be closely watched for signs of whether his mental acuity is failing.

Biden will travel to Madison, Wisconsin, to rally Democratic voters on Friday.

During the trip he will be interviewed by ABC News, part of a flurry of events during the next week aimed at showing Americans he still has the stamina to run against Republican candidate Donald Trump in the November 5 election.

While Biden insists he is staying in the race and that his health is not faltering, he is under enormous pressure to step aside and open a path for his 59-year-old vice president, Kamala Harris.

Some donors are making their displeasure known loudly, halting funding or looking at possible Democratic alternatives. Even some of Biden’s closest political allies, like former Speaker Nancy Pelosi, have raised questions about his health.

Several public opinion polls have shown Trump establishing a sizeable lead over the Democratic president since the debate, while a Reuters/Ipsos poll found one in three Democrats want Biden to quit the race.

The White House has blamed a cold for Biden’s shaky performance and Biden himself cited jet lag from back-to-back trips to Europe.

The ABC interview offers the likelihood of unscripted comments from Biden, who relies heavily on the use of a Teleprompter for his public remarks.

At Fourth of July holiday ceremonies on the White House South Lawn on Thursday night, Biden responded quickly when someone shouted at him to “keep up the fight”.

“You got me, man,” Biden responded. “I’m not going anywhere.”

Harris is a strong contender to take his place if Biden were to drop out, sources have said, though his allies believe he can still assuage the concerns of voters and donors.

Trump’s campaign and some of his allies have launched a pre-emptive political strike on Harris, moving swiftly to try to discredit her amid talk that she could eventually replace Biden as the Democrats’ nominee.

The Biden campaign showed no signs of slowing down, although the Trump team has overtaken it on fundraising.

The campaign announced it would spend $US50 million ($A74 million) on a media blitz for the month of July, “including strategic investments around key events that draw in large and politically diverse audiences like the 2024 Olympic Games and the Republican National Convention”.

Trump, 78, who made multiple false statements from the debate stage in Atlanta, falsely claimed in a video that was circulated on social media that he had driven Biden out of the race.

He made disparaging comments about Harris in the same video, which the Trump campaign stood by.