Amid a last dash by candidates courting crucial battleground states, the United States is bracing itself for an election where the outcome looks to be uncertain, possibly even disputed.
Some 24 hours before polls open today, Democratic Party candidate Joe Biden remained ahead of his Republican rival Donald Trump across the country.
But in a few battleground states crucial to winning the presidency, the former vice-president's lead is either very slender, or he is in effect in a tie with the President.
This means Mr Trump could still garner the majority of Electoral College votes to become the winner.
Analysts, however, do not expect election night to go smoothly, as millions of mail-in ballots - generally seen to favour Democrats - will potentially still be left to count.
This is not unusual; the election night result is normally called on the basis of trends and projections - not on a final official count. But the volume of mail-in ballots appears to be higher this year.
At least 92 million people have already cast their ballots in early voting - nearly twice as many as those who did so in 2016. Some 230 million Americans are eligible to vote in the presidential election.
For months, Mr Trump has been criticising mail-in balloting as prone to fraud - which experts say there is little or no evidence of.
On Sunday, Axios reported that the President had told confidants he would seize the opportunity to declare victory tonight as results come in, at a point when he is ahead of Mr Biden. Mr Trump denied that, but said: "I think it's a terrible thing when ballots can be collected after an election."
And signalling protracted legal battles, he added: "We're going to go in the night of, as soon as that election's over, we're going in with our lawyers."
This election looks different from 2016, when Mr Trump also trailed his rival Hillary Clinton but won the Electoral College by winning a handful of states by fewer than 100,000 votes all told, polling organisation Morning Consult said yesterday. Mr Biden's lead is 8 percentage points compared with Mrs Clinton's three points in 2016.
But Mr Nate Silver, founder of political analytics website Five Thirty Eight, said in a note yesterday: "Projected margins in the tipping-point states are considerably tighter than the margins in the national popular vote.
"More specifically, Joe Biden's lead in Pennsylvania - the most likely tipping-point state, according to our forecast - is solid but not spectacular: about five points in our polling average."
Pennsylvania has 20 votes in the Electoral College.
"Without Pennsylvania, Biden does have some paths to victory, but there's no one alternative state he can feel especially secure about," Mr Silver wrote.
Mr Trump was due to hold five rallies in four states in the campaign's final hours: North Carolina, Pennsylvania, Michigan and Wisconsin.
Mr Biden and his running mate Kamala Harris were due to focus on Pennsylvania and Ohio.
Meanwhile, fears of unrest and violence, especially if the outcome of the election is contested, have been rising.
At the weekend in New Jersey, a caravan of Trump supporters blocked a freeway.
In Texas, Trump supporters on a freeway swarmed around a Biden-Harris campaign bus; the Democratic Party cancelled events out of safety concerns.
In Washington, the White House perimeter is being fortified with a tall fence, and shops in the surrounding area have been boarded up. Some 250 National Guard troops have reportedly been put on standby.
