Donald Trump has admitted losing the US presidency would not be “easy”, as voters head to the polls in the final hours of a historic election.
The Republican incumbent said he had not yet thought about a concession or victory speech, as he addressed party workers at their headquarters in Arlington, Virginia.
Meanwhile, Democrat challenger Joe Biden headed back to his home state of Pennsylvania in a last-ditch bid to win over enough people to turn the state blue and reap its 20 electoral college votes.
He was bullish about the prospect of success, writing a note on the living room wall of the home he grew up in Scranton: “From this house to the White House with the grace of God.”
Americans now have just a matter of hours left to decide whether to re-elect Mr Trump or make him the first one-term president since George HW Bush failed to win four more years in 1992.
And in a bid to dispel attempts to invalidate the result, a federal judge has ordered the postal service to “sweep” facilities to “ensure that no ballots have been held up and that any identified ballots are immediately sent out for delivery”.
But Mr Trump is still pushing hard against counting deadlines being extended.
“You can’t have these things delayed for many days and maybe weeks, you can’t do that,” he said on Tuesday.
“The whole world is waiting, this country is waiting but the whole world is waiting.
“A lot of shenanigans, a lot of bad things happen with ballots when you say, ‘oh, let’s devote days and days.”
Looking ahead to the result, he added: “I’m not thinking about concession speech or acceptance speech yet. Hopefully, we’ll be only doing one of those two.
“And you know, winning is easy, losing is never easy – not for me, it’s not.”
Earlier, First Lady Melania Trump cast her ballot in Florida – another swing state the Republicans hope to hold, but where former president Barack Obama held a final campaign rally last night to pile the pressure on.
The first polls close from 7pm (12am GMT) – allowing counting to get underway quickly in battleground states including Georgia, North Carolina and Ohio.
Boarding has already gone up to cover shops and offices in California, Washington DC and New York in case violence breaks out.
While all eyes will be on who gets the top job, other races will decide how freely the next president can act.
Democrats are hoping to increase their majority in the House of Representatives, and flip a minimum of three seats in the US Senate to take control there.