US election: Do postal ballots lead to voting fraud?
Many US states are looking to make voting by post easier in the presidential election this November due to public health concerns over the coronavirus pandemic.
But the expansion of postal voting is contentious, and President Donald Trump has said postal ballots - know as "mail-in" ballots in the US - would lead to "the most corrupt election" in US history.
The president has even suggested delaying the election, which he doesn't have the power to do, to stop postal ballots leading to "inaccurate and fraudulent" results.
Mail-in ballots are very dangerous - there's tremendous fraud involved.
We've looked at the evidence and found very few cases of postal voting fraud.
Where can you vote by post?
In the 2016 US presidential election, nearly one quarter of votes were cast by post, and that number is expected to rise this time round.
Individual US states control their own voting rules for federal elections - and many are looking to increase postal voting to prevent large gatherings at polling stations on election day.
There are now six states planning to hold "all-mail" ballot elections this November - after California recently joined Utah, Hawaii, Colorado, Oregon and Washington - and more could follow.
These states will automatically send all registered voters postal ballots, which then have to be sent back or dropped off on election day - although some in-person voting is still available in certain limited circumstances.
About half of US states allow any registered voter to vote by post on request.
In the remaining states, you have to have a valid reason for voting by post - such as being over 65, being ill, or being away from the state you are registered to vote in.
Notably, President Trump has voted by post in the past, such as in Florida's 2020 primary election as he is a registered voter in the state but is living in Washington DC.
What evidence is there of fraud?
President Trump has said: "You get thousands and thousands of people sitting in somebody's living room, signing ballots all over the place."
Critics say people could vote more than once via absentee ballots and in person.
But there is no evidence of widespread fraud, according to numerous nationwide and state-level studies over the years.
There have been isolated cases of postal ballot fraud in the past, such as in the 2018 North Carolina primary, which was re-run after a consultant of the Republican candidate tampered with voting papers.
There was also a case earlier this year in New Jersey which saw two Democratic councillors charged with alleged fraud in relation to postal voting, after hundreds of ballots were found stuffed in a post box.
But these are rare incidents, and the rate of voting fraud overall in the US is between 0.00004% and 0.0009%, according to a 2017 study by the Brennan Center for Justice.
A voter fraud database collated by Arizona State University between 2000 and 2012, found 491 cases of postal ballot fraud out of hundreds of millions of votes.
And a Washington Post review of the 2016 election found one proven case of postal voting fraud.
Oregon has held postal elections since 2000 and has only reported 14 fraudulent votes attempted by mail.
There are provisions in place to prevent people from impersonating voters or stealing ballots - such as authorities checking that ballots have come from voters' registered address and requiring signatures on envelopes.
There have been suggestions that an increase in postal voting would help turnout among Democratic voters, but there is no strong evidence that either party would gain an advantage.