His encouragement follows a surge in Democratic requests to vote by mail in Florida, a critical swing state Mr Trump almost certainly must win to secure a second term in November.
Democrats currently have some 1.9 million Floridians signed up to vote by mail this November, far more than the Republicans’ 1.3 million, according to the Florida Secretary of State.
In 2016, both sides had around 1.3 million signed up before the general election.
“Whether you call it Vote by Mail or Absentee Voting, in Florida the election system is Safe and Secure, Tried and True. Florida’s Voting system has been cleaned up (we defeated Democrats attempts at change), so in Florida I encourage all to request a Ballot & Vote by Mail!,” Mr Trump tweeted on Tuesday.
White House press secretary Kayleigh McEnany rejected the notion the president had changed his views.
She said he supported absentee voting by mail for a reason, as opposed to states mailing out ballots to all voters regardless of whether they requested them. Most election officials say there is little effective difference between absentee voting and voting by mail.
Mr Trump elaborated on why he supports voting by mail in Florida, but not elsewhere.
“They’ve been doing this over many years and they’ve made it really terrific,” Trump said.
“This took years to do,” he added. “This doesn’t take weeks or months. In the case of Nevada, they’re going to be voting in a matter of weeks. And you can’t do that.”
Yet Florida hardly has a history of flawless elections, most notably in 2000 when the state’s disputed vote count had to be resolved by the US Supreme Court, delivering the presidency to George W Bush over Al Gore
Mr Trump cited a New York race as an example of what can go wrong, claiming no one could know the winner. In that race, a judge ruled on Monday that about 1,000 disputed ballots should be counted. That will likely not affect the outcome since the incumbent, longtime Democratic representative Carolyn Maloney, is leading her closest challenger by about 3,700 votes.
“I think they have to do the election over. That election is no good,” Mr Trump said.
More voters during this year’s primary elections opted to vote by mail, and several states relaxed restrictions for voting absentee through the mail. Mr Trump himself voted by mail in the Florida primary earlier this year.
Five states have relied on mail-in ballots since even before the coronavirus pandemic raised concerns about voting in person, but there is no evidence to support Mr Trump’s assertion that voting by mail leads to widespread fraud.
Mr Trump has gone so far as to suggest by tweet that the November election should be delayed “until people can properly, securely and safely vote”.
States that use mail-in votes exclusively say they have necessary safeguards in place to ensure no hostile foreign actors disrupt the vote. Election security experts say voter fraud is rare in all forms of balloting, including by mail.
With Florida’s large retirement population, voting by mail is expected to become a more popular option this November.
Florida is considered a must-win state for Trump’s reelection prospects. Its presidential contests are usually close, with Trump winning by just 1.2 percentage points in 2016, and George W. Bush winning Florida by just 537 votes in 2000.
