Democrat Joe Biden narrowly overtook President Donald Trump in the vote counts in Georgia and Pennsylvania, with the presidency hinging on the outcome of tight contests in key battleground states.
Neither candidate has reached the 270 Electoral College votes needed to win the White House, though Mr Biden has the advantage after eclipsing Mr Trump in Wisconsin and Michigan, two crucial Midwestern battleground states.
That left both campaigns increasingly focused on developments in Pennsylvania and Georgia, where Mr Biden had an advantage of more than 4,000 votes on Friday evening.
He has also moved ahead of the incumbent president in Pennsylvania although the race is still too close to call.
Officials in Georgia confirmed that a recount would be held because of the close margin in the state.
With millions of ballots yet to be tabulated, Mr Biden has already received more than 73 million votes nationally, the most in history
As Americans entered the third full day after the election without knowing who won the race, anxiety about the outcome was building.
With his pathway to re-election appearing to narrow, Mr Trump was testing how far he could go in using the trappings of presidential power to undermine confidence in the vote.
He has been spending Friday at the White House tweeting, watching results come in and continuing to cast unfounded doubt over the integrity of the election.
He said in a statement released by his campaign: “We believe the American people deserve to have full transparency into all vote counting and election certification.”
He added: “This is no longer about any single election. This is about the integrity of our entire election process.”
He threatened continued legal action, saying: “We will pursue this process through every aspect of the law to guarantee that the American people have confidence in our government.”
On Thursday, Mr Trump advanced unsupported accusations of voter fraud to falsely argue that his rival was trying to seize power in an extraordinary effort by a sitting American president to sow doubt about the democratic process.
Mr Biden spent Thursday trying to ease tensions and project a more traditional image of presidential leadership.
After participating in a coronavirus briefing, he declared that “each ballot must be counted.”
“I ask everyone to stay calm. The process is working,” Mr Biden said.
“It is the will of the voters.
“No one, not anyone else who chooses the president of the United States of America.”
Mr Trump showed no sign of giving up and was was back on Twitter, insisting the “US Supreme Court should decide!”
Mr Trump’s erroneous claims about the integrity of the election challenged Republicans now faced with the choice of whether to break with a president who, though his grip on his office grew tenuous, commanded sky-high approval ratings from rank-and-file members of the Republicans.
That was especially true for those who are eyeing presidential runs of their own in 2024.
Maryland Republican governor Larry Hogan, a potential presidential hopeful who has often criticised Trump, said unequivocally: “There is no defence for the President’s comments tonight undermining our Democratic process.
“America is counting the votes, and we must respect the results as we always have before.”
But others who are rumoured to be considering a White House run of their own in four years aligned themselves with the incumbent, including Senator Josh Hawley, who tweeted support for Mr Trump’s claims, writing that “If last 24 hours have made anything clear, it’s that we need new election integrity laws now.”
Mr Trump’s campaign engaged in a flurry of legal activity to try to improve the Republican president’s chances, saying it would seek a recount in Wisconsin and filing lawsuits in Pennsylvania, Michigan and Georgia.
Judges in Georgia and Michigan quickly dismissed Trump campaign lawsuits there on Thursday, when Mr Trump still held a small edge in Georgia — though Mr Biden was gaining on him as votes continued to be counted.
The same was true in Pennsylvania, where Mr Trump’s lead slipped and the former vice president moved ahead.
It is a form of voting that has skewed heavily in Mr Biden’s favour after Mr Trump spent months claiming without proof that voting by mail would lead to widespread voter fraud.
Mail ballots from across the state were overwhelmingly breaking in Mr Biden’s direction.
A final vote total may not be clear for days because the use of mail-in ballots, which take more time to process, has surged as a result of the coronavirus pandemic.
The Trump campaign said it was confident the president would ultimately pull out a victory in Arizona, where votes were also still being counted, including in Maricopa County, the state’s most populous area.
The Associated Press has declared Biden the winner in Arizona and said Thursday that it was monitoring the vote count as it proceeded.
He would have to win multiple suits in multiple states in order to stop vote counts, since more than one state was undeclared.
Some of the Trump team’s lawsuits only demand better access for campaign observers to locations where ballots are being processed and counted.
A judge in Georgia dismissed the campaign’s suit there less than 12 hours after it was filed.
And a Michigan judge dismissed a Trump lawsuit over whether enough Republican challengers had access to handling of absentee ballots
Biden lawyer Bob Bauer said the suits were legally “meritless”.
Their only purpose, he said “is to create an opportunity for them to message falsely about what’s taking place in the electoral process.”