Trump: "I've been talking about mail-in voting for

Trump: "I've been talking about mail-in voting for a long time. It's really destroyed our system. It's a corrupt system and it makes people corrupt."
Mr Trump has posted more than 70 tweets casting doubt on mail-in voting, referencing voter fraud or "rigged" elections since April.

But there is no evidence the system is corrupt.

Electoral fraud is very rare in the United States - the rate is less than 0.0009%, according to a 2017 study by the Brennan Center for Justice. There's no evidence to suggest it's been a major issue at this election either.

The president himself has voted by post in the past. He lived outside the state he was registered in, Florida, and requested a postal vote.

This is known as an absentee ballot, which Mr Trump has said he is in favour of because he believes it has better safeguards.

But he has made a distinction with other forms of mail-in voting, such as when states automatically send out ballots to all registered voters.

Oregon and Utah have done so successfully in previous elections.