Tuesday, 3 November was always going to be memorable, with those who love Donald Trump and those who hate him glued to the TV.
But it has become apparent that this will be an unusual election due to the time taken to find out who will be the next occupant of the White House.
Why are there delays to the election result announcement?
The 2016 election was called for Mr Trump at about 02:30 EST (07:30 GMT) after victory in Wisconsin put him over the 270 electoral votes needed.
This year is proving very different.
An unprecedented number of Americans - 97.1 million by the last day of campaigning on Monday, well over twice the number from 2016 - have voted by mail in response to coronavirus concerns and some states are counting ballots delivered after the election (so long as they are postmarked ahead of a given deadline).
In Washington state, for example, mail-in ballots can be counted until 23 November. In Alaska, state officials don’t even begin counting mail-in ballots until around 10 November.
Those two states are relatively unimportant for the final result in the presidential race as Washington is strongly Democrat and Alaska fairly solidly Republican, meaning neither is likely to upset the applecart.
However, swing states have also faced challenges reporting quickly due to the unprecedented influx of postal votes.
In Pennsylvania — key for Mr Biden and essential for Mr Trump — mail-in ballots can be counted three days after the polls close, following a battle that made it all the way to the Supreme Court.
Mr Trump’s campaign prematurely declared victory in the state and also filed a suit in the Supreme Court asking for the remaining ballots not to be counted.
The Trump campaign said that it was suing to temporarily stop the vote count in the Keystone State, citing a lack of “transparency” in the counting process.
Justin Clark, Trump's deputy campaign manager, said the campaign is “suing to stop Democrat election officials from hiding the ballot counting and processing from our Republican poll observers.”
He said the campaign wants "to temporarily halt counting until there is meaningful transparency and Republicans can ensure all counting is done above board and by the law."
What have Trump and Biden said?
Both candidates were well aware of the fact that there might be delays.
Mr Biden was urged by Hillary Clinton not to concede on election night "under any circumstances because I think this is going to drag out" and he has said that he will only accept “the full results”.
On election night, Mr Biden told his supporters to “keep the faith” and urged them to “be patient” as the counting continued. He spent the evening watching the returns come in from his home in Wilmington, Delaware, then drove downtown by motorcade to make his statement outside the Chase Center.
He told a gathering of supporters that his hopes for victory remain high despite the uncertainty and cautioned them that it could take a day or longer to know who had won. He told them: “Your patience is commendable.”
On Wednesday, Mr Biden urged the counting of all votes.
"Here, the people rule. Power can't be taken or asserted. It flows from the people," he said. "And it's their will that determines who will be president of the United States and their will alone. And now after a long night of counting, it's clear that we are winning enough states to reach 270 electoral votes needed to win the presidency.”
On Thursday, Mr Trump made a series of baseless claims, saying the process was “a major fraud on our nation.”
He cast the night as a disenfranchisement of his voters and said: “We will win this and as far as I’m concerned we already have won it… We’ll be going to the US Supreme Court - we want all voting to stop.”
In fact, there is no more voting - just counting.
Mr Trump had repeatedly stated that he might not accept the results at all. He is doing his utmost to warn of voter fraud and election rigging - something that experts say is extremely rare - and without offering hard evidence himself.
The Brennan Center for Justice says rates for voter fraud in elections it had studied ranged from 0.0003 per cent to 0.0025 per cent.
“We have to prepare for the very strong probability that an election unlike any other we’ve ever had might take a little longer to accurately count with integrity,” said David Becker, executive director and founder of the Washington DC-based non-partisan Center for Election Innovation & Research.
“More time being taken to report results is not an indication of a problem.”
When will the election be over?
Pennsylvania, Nevada, North Carolina and Georgia are among the key states yet to declare their results - but major developments are expected before noon eastern time (5pm UK time) on Saturday.
Arizona was declared a win for Mr Biden by both AP and Fox News, but the lead has diminished as more votes come in - a warning sign the state could still be in play. However the result could be confirmed as early as 11am eastern time (4pm UK), when a big batch of results from Maricopa County is due to be released.
Pennsylvania is pushing ahead despite Team Trump’s objections and is expected to deliver a result this weekend. As of 11am eastern time (4pm UK), Mr Biden was ahead by more than 30,000 votes in Pennsylvania, with further results expected to be uploaded at 11:30am (4.30pm).
If they give Mr Biden enough of a lead to avoid a recount and call the state in his favour, it would hand him 20 Electoral Colleges and the presidency should the victory be confirmed.
The Georgia vote has meanwhile been ruled too close to call, with Mr Biden ahead by just over 7,000 votes on Saturday. Secretary of state Brad Raffensperger has already announced a recount would be necessary to determine the winner.
With 99 per cent of votes counted in North Carolina, Mr Trump is on 50.1 per cent and Mr Biden just behind on 48.7 per cent.
An estimated 87 per cent of the Nevada vote has been counted, though uncounted ballots have continued to arrive. At the time of writing, Mr Biden is ahead by 1.8 points with a margin of 22,657.
The primaries earlier this year actually gave us some indication of how this might all play out.
By 17 March, almost half of all states, 24, had held primaries. Five of those states heavily used vote-by-mail, as they had in previous elections. They reported their results in an average of 6.4 days, according to data analysed by The Washington Post.
The other 19 had mainly in-person voting and reported results on average after 15 hours.
After 17 March, when the pandemic forced significant adjustments to voting systems, there were primaries in 23 more states, which took an average of four days to report nearly complete results. Nearly all of these states had traditionally relied on in-person voting.
New York processed 94 per cent of its votes within a few hours of polls closing. But counting the final six per cent of votes took more than 10 days and one race in particular - for the congressional seat held by long-term congresswoman Carolyn Maloney - took six weeks to be resolved.
That suggested from the start that it could take several days for the results to be clear, and, if both candidates accept the result, the matter will be solved.
What happens if Trump or Biden don’t accept the election result?
If either candidate is still not satisfied, a recount could be demanded.
In 2018, in Florida, a recount was demanded for three statewide races - for senator, governor and agriculture commissioner.
The machine recount was ordered on 10 November, with a deadline set for 8pm on 15 November.
That was still inconclusive, in the senate race, so Florida ordered its first ever recount by hand.
That was completed on 18 November and officially approved on 20 November - two weeks to the day after the 6 November vote.
But even a recount result may be unlikely to resolve the issue: Mr Trump has said he believes the election result could end up in the Supreme Court.
What would the Supreme Court involvement be?
This has happened before. In the 2000 election, Al Gore, the Democratic candidate, argued that his narrow margin of defeat in Florida should lead to a recount.
It took 36 days and the Supreme Court to decide against a recount to settle the contest in favour of Republican George W Bush. He, like Trump, had lost the popular vote.
Various legal challenges could emerge this year - everything from the identification requirements for postal voting to the legality of Covid-related changes to voting.
Is there a ‘hard deadline’ to all this?
Inauguration Day - always 20 January, or 21 January if that first date falls on a Sunday - is set by the Constitution under the 20th Amendment, enacted in 1933.
Prior to that, the “lame duck” period stretched on until March and caused untold problems.
In the "secession winter" after the election of Abraham Lincoln, 15th president James Buchanan sat back and watched as secessionists seized federal forts and arsenals. By March 1861, when Lincoln finally took office, the Civil War was almost lost before it had even begun.
And, in the midst of the Great Depression, Herbert Hoover’s lame duck period dragged on interminably and frustrated the public. In response, the 20th Amendment was proposed and adopted.
So 20 January 2021 is therefore considered the ultimate hard deadline.
And if there are still problems?
If the election result is not confirmed and accepted by then, the United States will be plunged into a deeply partisan constitutional crisis and we enter the realm of the unknown.
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