Joe Biden took a huge step Wednesday to capturing the White House, with wins in Michigan and Wisconsin bringing him close to a majority, but US President Donald Trump responded with a diatribe alleging mass fraud and demanding a halt to vote counting.
In a brief address on national television, flanked by US flags and his vice-presidential pick Kamala Harris, Biden said he wasn't yet declaring victory, but said that "when the count is finished, we believe we will be the winners."
By flipping the northern battlegrounds of Michigan and Wisconsin, Biden reached 264 electoral votes against 214 so far for Trump. By adding the six of Nevada, where he is narrowly ahead, he would hit the magic number of 270 needed to win the White House.
In stark contrast to Trump's increasingly heated rhetoric about being cheated, Biden sought to project calm, reaching out to a nation torn by four years of polarising leadership and traumatised by the Covid-19 pandemic.
"I know how deep and hard the opposing views are in our country on so many things," Biden, 77, said.
"But I also know this as well: to make progress we have to stop treating our opponents as enemies. We are not enemies. What brings us together as Americans is so much stronger than anything that can tear us apart."
American presidential elections are decided not by the popular vote but by securing a majority in the state-by-state Electoral College, which has 538 members.
US media organisations called Michigan for Biden after he took a lead of almost 70,000 with 97 percent of ballots counted. Earlier, Biden claimed Wisconsin, with a narrower but insurmountable lead.
This, along with Arizona – another Trump state that Biden flipped – put the Democrat within arm's reach of making Trump a one-term president.
Results were still being tabulated in Georgia, Nevada, North Carolina and Pennsylvania -- all close contests, as well as in reliably Republican Alaska. Counting has been complicated by the coronavirus pandemic and record numbers of mailed-in ballots that can take longer to process.
Trump claims being cheated
However, Trump, 74, claimed victory unilaterally and made clear he would not accept the reported results, issuing unprecedented complaints – unsupported by any evidence – of fraud.
"Last night I was leading, often solidly, in many key States, in almost all instances Democrat run & controlled," Trump tweeted. "Then, one by one, they started to magically disappear as surprise ballot dumps were counted."
Trump's campaign announced a lawsuit to try and suspend the vote count in Michigan, where it said its team was denied proper access to observe vote counting.
The campaign said it was also suing to halt the counting of votes in Pennsylvania – after the president called overnight for Supreme Court intervention to exclude the processing of mail-in ballots after the close of polls.
And it demanded a recount in Wisconsin, citing "irregularities."
The president's personal lawyer, Rudy Giuliani, spoke to the media in Philadelphia, Pennsylvania, accusing Democrats of sending in fraudulent ballots. He also provided no evidence.
"This is the way they intend to win," Giuliani said. "We're not going to let them get away with it."
Trump campaign manager Bill Stepien said they had won in Pennsylvania, despite the result still being calculated, and he rejected the call giving Biden a win in Arizona.
Campaign advisor Jason Miller told journalists that by the end of the week, Trump's reelection "will be clear to the entire nation."
'We have to be patient'
Unless one candidate notches up enough states for total victory earlier, the struggle could end up in Pennsylvania, which is likely to see the messiest counting process.
Here, Trump had a roughly 500,000 vote lead with an estimated 78 percent of the vote counted but votes were awaited from heavily Democratic parts of the state, promising to level things up.
"We have to be patient," Pennsylvania Governor Tom Wolf said. "We may not know the results today.
"There are millions of mail-in ballots," he said. "They're going to be counted accurately and they will be counted fully."
The Democratic governor shrugged off criticism from the White House over the slow vote count and said "our democracy is being tested in this election."
"Pennsylvania will have a fair election," he said. "And that election will be free of outside influences."
The tight White House race and recriminations evoked memories of the 2000 election between Republican George W. Bush and Democrat Al Gore.
That race, which hinged on a handful of votes in Florida, eventually ended up in the Supreme Court, which halted a recount while Bush was ahead.
The US Elections Project estimated total turnout at a record 160 million voters including more than 101.1 million early voters, 65.2 million of whom voted by mail.