An unprecedented number of mail-in ballots are expected as many states have made it easier to vote by mail to address concerns about public gatherings during the coronavirus pandemic.

Without evidence, Trump has repeatedly claimed increased mail voting would be rife with fraud, remarks that have deepened Democrats' fears that he will refuse to accept the election outcome should he lose.

U.S. President Donald Trump is privately reassuring Republicans anxious about his deficits to Democrat Joe Biden, noting there are three months until Election Day.