Washington (AFP)

Americans go to the polls on Tuesday, and more than 100 million of them have already voted early, by mail or in person, but the outcome of the presidential election is likely to be delayed.

To win, a candidate does not need to have a majority vote at the national level: he must obtain at least 270 of the 538 elected voters at the state level.

But uncertainties weigh on the ballot and the winner of this merciless battle between Republican President Donald Trump and Democrat Joe Biden, favorite in the polls, will not be known until Tuesday evening at the earliest, or even Wednesday.

Postal voting also risks delaying the count, as the counting of ballots arriving in the days following the ballot is possible in many states.

At what time will we receive the first results?

The first vote counts begin to be published after polling stations in parts of Kentucky and Indiana close at 6:00 p.m. local time (11:00 p.m. GMT).

Most states will close their polling stations by 9:00 p.m., paving the way for a steady stream of counts over the following hours, with some states and constituencies known to be faster than others in this exercise.

California, the country's most populous state, votes until 4:00 a.m. GMT Wednesday and Hawaii and Alaska, which weigh little in terms of large voters, vote even later.

Which states to watch?

As the polls are fairly clear on voting intentions in 38 of the 50 US states, 12 contested states need to be watched.

The first will come from the eastern states of the country: Georgia where polling stations close at 7:00 p.m. (00:00 GMT Thursday), Florida where they close depending on the constituencies at 7:00 p.m. or 8:00 p.m. and North Carolina (7:30 p.m.).

Then comes Arizona (west) where voting ends at 02:00 GMT Wednesday.

Based on US media projections, it's possible that Joe Biden will be announced as the winner of over 270 voters if he wins Florida and two more of those four states.

On the other hand, if Donald Trump wins these four states, the end result would remain uncertain.

How is the winner chosen?

Officially, the name of the winner is not announced until each state has certified their vote counts, which, given the massive early voting, could take a week or more in places.

But the name of the winner is traditionally given by the mainstream American media on election night, based on projected votes, constituency by constituency.

They determine the winner in each state and then finally the whole ballot, when it appears that one candidate has no mathematical chance of overcoming his vote deficit and the other candidate is sure to get the magic number of 270 great voters.

Ronald Reagan's victory in 1980 was announced as early as 8:15 p.m. (01:15 GMT), but Donald Trump's in 2016 was not clear until much later, when the tallies showed he had won Pennsylvania.

In 2000, it was Florida that decided the election, by a few hundred votes.

It took 36 days for George W. Bush to be declared the winner against Democrat Al Gore, in an unprecedented arbitration by the Supreme Court.

When will we know who won?

It could be 11:00 p.m. (4:00 a.m. Wednesday) or earlier if Biden clearly wins the first four contested states.

Otherwise, it will depend on other key states, which could go on.

In the crucial state of Pennsylvania, polling stations close at 8:00 p.m. (1:00 a.m. Wednesday).

But local officials have warned that the early vote count could delay the outcome until Wednesday or later.

The same could happen in Michigan, Wisconsin and other key states.

And if the ballots need to be checked or recounted, it may take days or even weeks.

© 2020 AFP