U.S. President Donald Trump on Thursday raised the possibility of delaying the nation’s November presidential election despite its date being enshrined in the U.S. Constitution.

Trump, without evidence, repeated his claims of mail-in voter fraud and raised the question of a delay, writing: “delay the election until people can properly, securely and safely vote???”

Representatives for the White House did not immediately respond to a request for comment.

Trump has cast doubt on the legitimacy of mail-in ballots, which have been used in far greater numbers in primary elections amid the coronavirus pandemic. He has also made unsubstantiated allegations that voting will be rigged and has refused to say he would accept official election results if he lost.

Democrats, including presumptive presidential nominee Joe Biden, have already begun preparations to protect voters and the election amid fears that Trump will try to interfere with the Nov. 3 election.