US President Donald Trump has refused to commit to a peaceful transfer of power if he loses November’s election.
“Well, we’ll have to see what happens,” the president told a news conference at the White House. “You know that.”
Mr Trump voiced concern about ballots, an apparent reference to postal voting, which he argues is susceptible to fraud even though he has voted in this way.
More states are encouraging mail-in voting, citing the need to keep voters safe amid the coronavirus pandemic.
Mr Trump was asked by a reporter on Wednesday evening if he would commit to a peaceful transfer of power “win, lose or draw” to Democrat Joe Biden.
“I’ve been complaining very strongly about the ballots,” Mr Trump, a Republican, said. “And the ballots are a disaster.”
When the journalist countered that “people are rioting”, Mr Trump interjected: “Get rid of the ballots, and you’ll have a very – you’ll have a very peaceful – there won’t be a transfer, frankly, there’ll be a continuation.”
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Back in 2016, Mr Trump also refused to commit to accepting the election results in his contest against the Democratic candidate, Hillary Clinton, which she characterised as an attack on American democracy.
He was eventually declared the winner, although he lost the popular vote by three million, an outcome on which he still cast doubt.
Last month, Mrs Clinton urged Mr Biden this time not to concede defeat “under any circumstances” in a close race on election night.
She raised the scenario that Republicans would try “messing up absentee balloting” and mobilise an army of lawyers to contest the result.
Conservatives have accused Mr Biden himself of stoking civil unrest over the election by saying in August: “Does anyone believe there will be less violence in America if Donald Trump is re-elected?”
Earlier on Wednesday, the US president defended his decision to seek the appointment of a new Supreme Court justice before the vote to fill the vacancy left by the late Ruth Bader Ginsburg, saying he expects the election results to end up before the court.
“I think this [the election] will end up in the Supreme Court, and I think it’s very important that we have nine justices,” the president said.
“I think it’s better if you go before the election, because I think this scam that the Democrats are pulling, it’s a scam, the scam will be before the United States Supreme Court.”
Mr Trump was apparently referring again to his much-disputed claims that mail-in ballots are vulnerable to fraud.
The president has said he will name a female nominee for the court this Saturday. She would replace Justice Ginsburg, who died last Friday.
Mr Trump’s supporters hope his nominee, if confirmed by the US Senate, will cement a 6-3 conservative ascendancy on the nation’s highest court for the forseeable future.
Every losing US presidential candidate in modern times has conceded, even in very tight electoral results.
These include 1960 when John F Kennedy narrowly beat Richard Nixon and in 2000 when George W Bush beat Al Gore in Florida.