WASHINGTON (REUTERS) - US President Donald Trump has been dealt a new setback in his desperate bid to overturn the United States election as a federal judge dismissed a lawsuit filed by his campaign that sought to throw out millions of mail-in votes in Pennsylvania.

US District Court Judge Matthew Brann last Saturday (Nov 21) ruled that Mr Trump's campaign had failed to demonstrate there had been widespread voting fraud in the Nov 3 election, which Mr Trump lost to Democrat Joe Biden.

"This Court has been presented with strained legal arguments without merit and speculative accusations," Judge Brann wrote.

He added that he "has no authority to take away the right to vote of even a single person, let alone millions of citizens".

The lawsuit, spearheaded by Mr Trump's personal lawyer Rudy Giuliani, sought to stop officials from certifying Mr Biden's victory in the state, arguing that some counties wrongly allowed voters to fix errors on their mail ballots.

Mr Giuliani, who made his first courtroom appearance in 30 years for a hearing in the case on Tuesday, did not immediately respond to a request for comment. The Biden and Trump campaigns also did not immediately respond to queries.

Mr Giuliani and other Trump lawyers floated a variety of conspiracy theories at a news conference last Thursday as they alleged that the election was marred by widespread voter fraud.

But they have had little success in court.

Mr Trump and his allies have now won two election-related cases and lost 34, according to Democratic election lawyer Marc Elias.

Democrats said Saturday's scathing verdict was further proof that those charges are false.

Mr Giuliani has signalled in legal filings that he will pursue an appeal, but he has little time to do so before the state formalises Mr Biden's victory on Monday.

"As far as litigation goes, I believe this is the end of the line for them," said Mr Benjamin Geffen of the Public interest Law Centre, who was also involved in the case.

Mr Trump is seeking to invalidate or change the election results through recounts and direct pressure on lawmakers in several states. He would need to prevail in at least three states to prevent Mr Biden from being sworn in as president on Jan 20 - an unprecedented action.

In Michigan, Republicans wrote to state authorities last Saturday asking them to wait 14 days to certify Mr Biden's victory to allow for an audit of ballots in Wayne county, which includes the majority-black city of Detroit.

The letter cited allegations of "irregularities" that have not been substantiated. Mr Biden won 154,000 more votes than Mr Trump in Michigan.

That effort faces long odds. A spokesman for Michigan's top election authority said state law does not allow for audits before the vote is certified, which is due to take place on Monday. Allegations of widespread fraud have been found to be baseless, the spokesman said.

Two leading Republican Michigan lawmakers who came to Washington at Mr Trump's behest said after meeting him last Friday that they had no information that would change the outcome of the election in the state.

In Wisconsin, an official said poorly trained observers for the Trump campaign were slowing a partial recount by challenging every ballot and raising other objections.

"Observers are disruptive. They are asking question after question, telling the tabulators to stop, stop what they're doing and that is out of line, that's not acceptable," Milwaukee County Clerk George Christianson told reporters.

A manual recount and audit in Georgia confirmed Mr Biden last Friday as the winner in the southern state, the first Democratic presidential candidate to win Georgia in nearly three decades.

The Trump campaign has two business days to request a recount in Georgia. Mr Trump's legal team has also said it plans a lawsuit in the state, but has not provided specifics.

Mr Trump's accusations have continued to inflame his hard-core Republican base.

Hundreds of supporters gathered at the statehouse in Atlanta last Saturday, with video posted online showing speakers denouncing the media for calling Mr Biden the election winner, as well as state Republican leaders for certifying the results.

Police in riot gear were deployed to separate them from counter-protesters who gathered nearby.

The General Services Administration, run by a Trump appointee, has not recognised Mr Biden's victory, preventing his team from gaining access to government office space and funding normally provided to an incoming administration ahead of Inauguration Day on Jan 20.

Critics say the delay and Mr Trump's refusal to concede have serious implications for national security and the fight against the coronavirus, which has killed nearly 255,000 Americans.

Mr Biden, who has denounced Mr Trump's attempt to reverse the election results as "totally irresponsible", spent Saturday meeting transition advisers and attending church.

Mr Trump took part in a virtual summit of the 20 biggest world economies and then went to play golf at his club in Sterling, Virginia.