Even after the astonishing blur of events of the past few months, the electorate is divided down the middle, both nationally and in the seven battleground states expected to determine the outcome.
The winner might not be known for days after Tuesday's vote.
Opinion polls for months have shown Kamala Harris and Donald Trump running neck-and-neck. (AP PHOTO)
Former president Trump, a 78-year-old Republican, survived two assassination attempts weeks after a New York City jury made him the first former US president to be convicted of a felony.
Vice-President Harris, 60, was catapulted to the top of the Democratic ticket in July - giving her a chance to become the first woman to hold the world's most powerful job - after President Joe Biden, 81, ended his re-election bid following a disastrous debate performance against Trump that prompted calls from his party to drop out.
For all of that turmoil, the contours of the race have changed little, and opinion polls for months have shown Harris and Trump running neck-and-neck.
More than 80 million voters have already cast ballots, and both candidates plan to spend the campaign's final hours doing everything they can to ensure their remaining supporters vote on Tuesday.
"It's ours to lose," Trump told supporters gathered in Raleigh, North Carolina, one of the seven battleground states.
"If we get everybody out and vote, there's not a thing they can do."
"It's ours to lose," Donald Trump told supporters in the battleground state of North Carolina. (AP PHOTO)
In Scranton, Pennsylvania, Harris urged several hundred volunteers to enjoy the moment as they headed out to knock on doors.
"We all have so much more in common than what separates us," she said.
Harris's campaign team believes the sheer size of its voter mobilisation efforts, including knocking on hundreds of thousands of doors in each of the swing states, is making a difference.
"We are feeling very good about where we are right now," campaign chair Jen O'Malley Dillon told reporters.
The campaign says its internal data shows that undecided voters, particularly women, are breaking in their favour, and says it has seen an increase in early voting among core parts of its coalition, including young voters and voters of colour.
Trump's campaign has outsourced most of the work to outside groups, including one run by tech billionaire Elon Musk, which have focused on contacting supporters who do not reliably take part in elections.
"We all have so much more in common than what separates us," Kamala Harris said in Pennsylvania. (AP PHOTO)
Aides said they were monitoring early-voting results that show more women have voted than men - a potential concern, given Harris's emphasis on abortion rights.
"Men must vote!" Musk wrote on his X social media platform.
Trump said he was heartened by robust early-voting numbers in hurricane-ravaged part of North Carolina, which have leaned Republican in past elections.
One official said they thought Trump would carry North Carolina, Georgia and Arizona, which would still require him to carry one of battleground states in the Rust Belt -- Michigan, Wisconsin or Pennsylvania - to win the White House.
Republicans also appeared to be posting strong early-vote results in Nevada.
Trump and his allies, who falsely claim his 2020 defeat was the result of fraud, have spent months laying the groundwork to again challenge the result if he loses.
Early-voting results show more women have voted than men, a potential concern for Donald Trump. (AP PHOTO)
He has promised "retribution" if elected, spoken of prosecuting his political rivals and described Democrats as the "enemy within".
Trump believes concerns about the economy and cost of living will carry him to the White House.
After visiting Raleigh, he will campaign in Reading and Pittsburgh in Pennsylvania and Grand Rapids, Michigan, before returning to Palm Beach, Florida, to vote and await election results.
Harris will campaign in five Pennsylvania cities, ending the day with a rally in Philadelphia, which will include performances by Lady Gaga, Ricky Martin and Oprah Winfrey.
She is expected to spend election night at Howard University in Washington, a historically Black college that is her alma mater.
Pennsylvania is the biggest prize among the battleground states, offering 19 of the 270 electoral college votes a candidate needs to win the presidency.
