US President Donald Trump has for the first time floated a "delay" to the November 3 presidential election, as he makes unsubstantiated allegations that increased mail-in voting will result in fraud.
The dates of presidential elections - the Tuesday after the first Monday in November in every fourth year - are enshrined in federal law and would require an act of Congress to change.
The Constitution makes no provisions for a delay to the January 20, 2021 presidential inauguration.
"With Universal Mail-In Voting (not Absentee Voting, which is good), 2020 will be the most INACCURATE & FRAUDULENT Election in history. It will be a great embarrassment to the USA. Delay the Election until people can properly, securely and safely vote???" Trump tweeted on Thursday.
Democratic Representative Dan Kildee said Trump was "peddling lies" and his aim was to stay in power.
"Don't let it happen. Every American -- Republican, Independent and Democrat -- should be speaking out against this President's lawlessness and complete disregard of the Constitution," he wrote on Twitter.
US Senator Tom Udall, also a Democrat, tweeted "there is no way @POTUS can delay the election. We shouldn't let him distract us from his COVID19 incompetence".
Trump's tweet came on a day of bad economic news - the government reported that the US economy shrank at a dizzying 32.9 per cent annual rate in the April-June quarter, by far the worst quarterly plunge ever.
The coronavirus outbreak has shut down businesses, thrown tens of millions out of work and sent unemployment surging to 14.7 per cent.
There is no evidence of widespread voter fraud through mail-in voting, even in states with all-mail votes.
Five states already rely exclusively on mail-in ballots, and they say they have necessary safeguards in place to ensure that a hostile foreign actor doesn't disrupt the vote.
Election security experts say that all forms of voter fraud are rare, including absentee balloting.
Trump has increasingly sought to cast doubt on November's election and the expected surge in mail-in and absentee voting as a result of the coronavirus pandemic.
And Trump has called remote voting options the "biggest risk" to his re-election.
His campaign and the Republican Party have sued to combat the practice, which was once a significant advantage for the GOP.
Trailing in public and private polls, Trump refused in an interview just weeks ago with Fox News to commit to accept the results of the upcoming White House election, recalling a similar threat he made weeks before the 2016 vote.
"I have to see. Look ... I have to see," Trump told moderator Chris Wallace during a wide-ranging interview on Fox News Sunday.
"No, I'm not going to just say 'yes.' I'm not going to say 'no,' and I didn't last time, either."
Last month, Trump told supporters in Arizona that "this will be, in my opinion, the most corrupt election in the history of our country".
Just months ago, in April, Trump had ruled out the prospect of trying to change the election.
Australian Associated Press
