We know that early voting in the US election has soared this year, with turnout so far already at half the 2016 total. Part of that is down to voters wanting to avoid potentially crowded polling stations during the coronavirus pandemic.

But strong engagement with who wins is also a factor, and there are signs voter participation could be the highest in a century.

Nearly 48 million of the 70 million votes already cast have been by post (the other option is in-person voting, where people cast their ballots at a polling station ahead of election day.)

But Donald Trump and some of his supporters have repeatedly tried to undermine the validity of postal voting.

On Tuesday the president said it would be “inappropriate” to take extra time to count mail-in votes, stating: "It would be very, very proper and very nice if a winner were declared on November 3, instead of counting ballots for two weeks, which is totally inappropriate and I don't believe that that's by our laws

The huge number of ballots means they could take days or even weeks to count, experts say. However, the president is wrong to suggest it's illegal: states have until 8 December - known as the "safe harbor" deadline - to finalise their tallies.