US Attorney General William Barr said on Tuesday that the Justice Department has not found evidence of widespread voter fraud that would change the outcome of the 2020 presidential election.
His comments come despite President Donald Trump’s repeated claims that the election was stolen, and his refusal to concede his loss to president-elect Joe Biden.
Mr Barr, one of Mr Trump's strongest allies, said lawyers and FBI agents had been following up specific complaints and information they had received, but found no evidence that would change the election result.
Before the election, he repeatedly raised the notion that mail-in voter fraud could be especially vulnerable to fraud during the coronavirus pandemic, as Americans feared going to polling centres.
Last month, Mr Barr issued a directive to US lawyers across the country allowing them to pursue “substantial allegations” of any voting irregularities before the 2020 presidential election was certified, despite no evidence at that time of widespread fraud.
That memorandum gave prosecutors the ability to go around long-standing Justice Department policy that normally prohibit such actions before the election was certified.
Soon after it was issued, the department’s top elections crime official announced he would step down because of the directive.
The Trump campaign team led by Rudy Giuliani has been alleging without evidence a widespread conspiracy by Democrats to dump millions of illegal votes into the system.
It has filed lawsuits in battleground states alleging that partisan poll watchers did not have a clear enough view at some polling sites and therefore something illegal must have happened.
The claims have been repeatedly dismissed, including by Republican judges who have ruled that the suits lacked evidence.
Local Republicans in some battleground states have followed Mr Trump in making similar unsupported claims.
He has railed against the election in tweets and in interviews, although his own administration has said the 2020 election was the most secure ever.
Mr Trump recently allowed his administration to begin the transition over to Mr Biden, but he has refused to admit that he lost.
The issues his campaign and its allies have pointed to are typical in every election: problems with signatures; secrecy envelopes; postal marks on mail-in ballots; and the potential for a small number of ballots to be miscast or lost.
But they have also requested federal probes into the claims.
Lawyer Sidney Powell has spun fictional tales of election systems flipping votes, German servers storing US voting information and election software created in Venezuela “at the direction of Hugo Chavez", the Venezuelan president who died in 2013.
Ms Powell was removed from the legal team after an interview she gave where she threatened to “blow up” Georgia with a “biblical” court filing.
Mr Barr did not name her specifically but said: “There’s been one assertion that would be systemic fraud and that would be the claim that machines were programmed essentially to skew the election results.
"And the Department of Homeland Security and Department of Justice have looked into that, and so far we haven’t seen anything to substantiate that."
He said people were confusing the use of the federal criminal justice system with allegations that should be made in civil lawsuits.
Mr Barr said a solution for those complaints would be a top-down audit by state or local officials, not the US Justice Department.
“There’s a growing tendency to use the criminal justice system as sort of a default fix-all, and people don’t like something they want the Department of Justice to come in and investigate,” he said.
Mr Barr said that first of all there must be a basis to believe there was a crime to investigate.
“Most claims of fraud are very particularised to a set of circumstances or actors or conduct," he said.
"They are not systemic allegations and. And those have been run down; they are being run down.
“Some have been broad and potentially cover a few thousand votes. They have been followed up on.”