A new movie that pushes dubious and widely debunked conspiracy theories to bolster Donald Trump's claim that he was robbed of a second term as president has become a surprise hit at the US box office.

Despite warnings by experts, "2000 Mules," a film by Dinesh D'Souza -- who was convicted of violating campaign finance laws before being pardoned by the former president -- has garnered more than $1.2 million at the box office since its release in late May.

With large buckets of popcorn in hand, a group of elder moviegoers crowd into a matinee screening in a cinema in a commercial district in Virginia.

Passing by theaters showing the adventures of "Doctor Strange" or the latest "Sonic the Hedgehog" movie, the senior citizens settle down in front of the documentary promising to "expose widespread, coordinated voter fraud in the 2020 election, sufficient to change the overall outcome."

'Lifeblood of democracy'

The film opens with footage of anonymous voters enthusiastically slipping their ballots into boxes stamped with the American flag, while D'Souza tells the audience that "elections are the lifeblood of our democracy."

But, he says as the background darkens, the 2020 election "haunts the American mind."

Like millions of Americans, including former president Trump, D'Souza voices the debunked belief that the Democrats rigged the result of the last presidential election, relying on the widespread use of mail-in ballots during the Covid-19 pandemic.

"We can't move on unless we know the truth," the director says in his voiceover.

In an attempt to prove his theory, which has been rejected by all relevant US authorities, D'Souza shows himself, leaning on a kitchen counter and phoning a group based in Texas called True the Vote, which claims to "support election integrity." A meeting is arranged.

'A cartel'

In a kind of hangar packed with computer servers, two members of the group claim to have proof of the existence of a well-planned operation which, "like a cartel," hired "mules" to stuff ballot boxes in a series of states that were key to Joe Biden's victory in 2020.

To validate their hypothesis, they rely on vast troves of anonymous location data from smartphone apps, which they claim show the comings and goings of these "mules" between the headquarters of various NGOs and ballot boxes.

It's a "heist" and "a crime," says the outraged D'Souza.

In the theater in Virginia, the audience is sold.

"It's like a nuclear bomb," says one man.

The theories pushed in the movie have been seriously questioned by multiple disinformation experts.

They say that a delivery man, a taxi driver, or a postman working in the neighborhood could easily have been mistaken for people making such nefarious trips.

But for Trump and his supporters, this is the ultimate proof of the fraud they have been decrying for a year and a half.

"They rigged and stole the 2020 election, we cannot be okay with this, we cannot simply move on," says D'Souza as the film ends.

And as the first notes of the American national anthem play, he issues a call to action: "The America we love needs us now more than ever."