Trump declared, "this is going to be the greatest election disaster in history".
On Thursday morning, Trump used his attacks to suggest he may delay the election - an action he has no control over.
Visit Business Insider's homepage for more stories. Officials dismissed the possibility of foreign powers being able to interfere on a mass scale to produce and send fake ballots to voters and election authorities, a source said.
"This action undermines the democratic processes and freedoms that have underpinned Hong Kong's prosperity", she said, according to a transcript of the press conference produced by the White House.
A split Michigan Supreme Court on Friday declined to hear a case that sought to extend the state's deadline to receive absentee ballots - a decision that left one dissenting justice "baffled and troubled" ahead of the November presidential election in the swing state.
For some election experts and Democrats, the prospect of similar uncertainty is especially worrisome this year, given Trump's frequent declarations that mail-in voting is fraudulent and a "threat" to his re-election.
The move was widely seen as a setback for the pro-democracy movement that has been building there while China tightens its grip on Hong Kong.
The long-time Republican supporter said: "President Trump needs to be told by every Republican in Congress that he can not postpone the federal election".
"Given the importance that absentee voting will have on the upcoming general election, I am baffled and troubled by the majority's vote to deny leave to appeal here", Justice Richard Bernstein wrote.
Calebresi continued on to explain the history of Election Day and cited more laws to prove why canceling the fall election would be unconstitutional and illegal.
In defending his proposal, Trump clarified that he is keen on a free and credible election, in which the results, as always, are known on Election Night, "not days, months or even years".
The city saw a huge surge of mail-in ballots this year during the coronavirus pandemic - 403,000, compared with 23,000 in the 2016 primary.
"Mail-in ballots will lead to the greatest fraud", he stated, without proof.
In some states, the ballots can be accepted several days after Election Day, as long as they are postmarked before polls closed.
But Mr. Patel said thousands of voters never received ballots, and about 25% of people who voted by mail had their ballots rejected.
That does not mean The Associated Press news agency and other news organisations will not call a victor.
Trump's allegations that mail-in voting leads to increased fraud are unsubstantiated.