Donald Trump privately admitted he lost to Joe Biden just days after the 2020 election but kept insisting to Americans he won, documentary Stopping the Steal claims

Donald Trump admitted that he lost the 2020 election in the days after the vote took place, a new documentary claims.

'Stopping the Steal' says the former president was watching Joe Biden on TV while in the White House when he said: 'Can you believe I lost to this f**king guy?'

The claim in the documentary, by director Dan Reed, will likely cause fresh embarrassment for Trump, who became embroiled in an argument earlier this month for admitting he lost in 2020.

Trump said in early September that Biden beat him 'by a whisker', sparking desertions from his MAGA supporters and a sharp U-turn from the former president.

Stopping the Steal, which is out on Tuesday on HBO, describes the events leading up to the January 6 insurrection at a time when Trump's allies are trying to move on from it due to the election on November 5.

The film includes stinging criticism of Trump from his Attorney General Bill Barr who says the former president's conduct that day was 'despicable'.

In a brutal put-down, Barr says that when he saw the fringe lawyers Trump turned to after losing the election, he thought they looked like a 'barroom scene from Star Wars'.

Reed's previous films include Finding Neverland, the bombshell documentary about Michael Jackson, and The Truth vs Alex Jones about the defamation trials brought against the Infowars host that led to a $1.5 billion judgment against him.

This time, Reed focuses on Trump's refusal to admit defeat in 2020 and the event which led to a mob of his supporters storming the US Capitol on January 6, 2021.

Among those interviewed in Stopping the Steal is Alyssa Farah Griffith, the Trump White House director of strategic communications.

She says it was a 'very odd time' when a sitting president loses an election but did not concede and called the result a fraud.

In the documentary, she says: 'My office is just right around the corner from the Oval Office.

'I remember popping my head in and he's (Trump) watching Fox News and Joe Biden's on and he says: "Can you believe I lost to this effing guy?"

Farah Griffith did not give an exact date for when Trump said this, but in the timeline of the film it appears to have been within a few days of the vote.

Trump repeatedly denied he lost in 2020 but earlier this month told podcaster Lex Fridman that Biden 'beat us by a whisker', adding that it was a 'terrible thing'.

His comments sparked fury among hardcore Trump supporters including white nationalist and Holocaust denier Nick Fuentes.

Fuentes ranted on his podcast: 'So, why did we do Stop the Steal? Why did anyone go to January 6? Why did any one go to jail?'

He said Trump should have made his admission publicly 'before 1,600 people got charged' with crimes related to the insurrection.

Fuentes accused Trump of a 'tremendous betrayal' and a 'callous indifference to the sacrifices that his supporters made on his behalf'.

Following the uproar, Trump claimed his comments were meant 'sarcastically' and that he didn't lose.

Stopping the Steal includes vivid descriptions of election night in 2020 from people like Stephanie Grisham, the Trump White House communications director.

She says that by 2am when Fox News called Arizona for Biden and it looked like he was going to win, the White House was a mess.

Grisham says: 'The president was standing in the middle of this crowd of people and it was just chaos

'Everyone's yelling, Trump's waving a piece of paper in his hand, he's very angry. When he's pissed you don't want to even get in his line of vision.

'All of a sudden it was like a light switch, everybody started heading downstairs for him to speak'.

Trump claimed in his speech he had been the victim of fraud, and said: 'Frankly, we did win this election'.

Grisham says: 'When he started down that road of "frankly we won" I was devastated.

'I was so disappointed in my president. I thought how could you do this to the country and leave everyone hanging like this. I started to cry, I was pissed.'

Barr describes Trump's comments as 'very dangerous', one of many blunt comments about his former boss.

In the weeks following the election Barr investigated dozens of Trump's increasingly outlandish claims of fraud but couldn't find any evidence to back them up.

Barr told Trump it was 'bulls**t' but Trump ignored him and turned to people like Sidney Powell and former New York City mayor Rudy Giuliani, who both indulged in baseless conspiracy theories about communist plots from Venezuela.

During a notorious meeting at the White House in December 2020, Powell, Trump and others discussed using the military to seize voting machines.

Looking around at the people Trump was associating with, Barr tells the documentary they were so outlandish that they looked like a 'barroom scene from Star Wars'.

Barr also describes Trump's fury after he put out a statement saying that he couldn't find any evidence of election fraud.

'I went down to the Oval Office, the president was as mad as I've ever seen him,' he says.

'He was flushed, he was breathing heavily. He said why did you say this?

'I said because it's the truth. He said: "You pulled the rug out from under me, this is killing me. You must hate Trump".

'(I said) I don't hate you Mr President... you wheeled out this clown car, you wasted five or six weeks on this bulls**t theory. People just shoveling this s**t out to the American people'.

With a laugh, Barr, who quit soon after the meeting, adds that Trump was 'very resentful'.

Turning to January 6 itself, Barr says he is 'completely outraged' by the fact Trump watched events unfold on TV for two hours but did nothing.

'I felt he did precipitate the whole affair, that was outrageous,' Barr says.

According to Barr, Trump's pressure campaign on his Vice President, Mike Pence, to stop the certification of the vote in Congress was 'despicable'.

'The president's behavior was a betrayal of his supporters. What he did was irresponsible and shameful,' he says.

Among the others to criticize Trump is Rusty Bowers, the former speaker of the Arizona House of Representatives.

He recalled being called by Trump and Giuliani, who was working as Trump's personal lawyer at the time, who asked to reject the vote that showed Biden winning the state narrowly.

When Bowers asked Giuliani for proof he said he would get it to him - but it never came.

Recounting the conversation, Bowers says: 'The dude (Rudy) is straight up asking me to throw the election'.

Bowers refused and was subjected to an onslaught of abuse and threats from Trump supporters, who turned up at his home and called him a pedophile.