President Donald Trump continued his assault on the integrity of the U.S. elections during the first presidential debate Tuesday, spreading falsehoods about the security of voting and misrepresenting issues with mail ballots.

In the final segment of the contentious debate between Trump and Democrat Joe Biden, Trump launched into an extended argument against mail voting, claiming without evidence that it is ripe for fraud and suggesting mail ballots may be "manipulated."

"This is going to be a fraud like you've never seen," the president said of the massive shift to mail voting prompted by the coronavirus pandemic.

Trump's riff was laden with misstatements and inaccuracies. Mail voting has proved to be safe and secure in the five states that already use it broadly. And while some irregularities and errors have occurred in the early vote, Trump on Tuesday mischaracterized those incidents. 

His comments come as his reelection campaign and the Republican Party have begun challenging the way those ballots are being processed and preparing for broad legal battles after Election Day. 

A look at Trump's claims and the facts. 

—Trump accused Philadelphia election officials of inappropriately keeping his campaign's poll monitors from observing voters filling out mail ballots at a voting center Tuesday. He was repeating an accusation he and his son had made earlier this week — and election officials have disputed. Election lawyers note Trump campaign's watchers had no legal right under state law to observe citizens filling out mail ballots.

—Trump cited a case of military ballots marked for him being thrown in the trash as evidence of a possible plot to steal the election. But he didn't mention the strange details of the case. County election officials say that the seven ballots, along with two unopened ones, were accidentally tossed  in an elections office in a Republican-controlled county by a single contract worker and that authorities were swiftly called.

—Trump pointed to problems that have arisen as states rush to adapt to mail balloting — mainly in his native New York, where elections officials sent error-riddled mail ballots this week and a slow count left the outcome of multiple congressional primaries up in the air in June. But he falsely claimed that the outcome of one of those races, the primary won by Democratic Rep. Carolyn Mahoney, was fraudulent.

—Trump claimed a West Virginia mail worker was "selling ballots." That drew a clarification from West Virginia's Republican secretary of state, Mac Warner, who noted the case involved a postal worker altering eight absentee ballot applications during the state's primary election earlier this year. Five ballot requests had party affiliations changed from Democrat to Republican. On the other three requests, the voters' GOP party affiliation was not changed but the postal worker circled the word "Republican" in a different color ink than was used on the forms. The carrier pleaded guilty to election fraud and injury to the mail in July. 

— Voter fraud is rare in the United States. An analysis by the Brennan Center for Justice found Americans were more likely to be struck by lightning than to commit voter fraud.

Still, Trump continued to sow distrust and again refused to commit to avoid declaring victory if the count goes past Election Day, as expected. Last week his refusal during a news conference to commit to a peaceful transition alarmed many.

Biden tried to lower the temperature about accepting the voters' will. "I will accept it, and he will, too. You know why?" Biden said. "Because once the winner is declared once all the ballots are counted, that'll be the end of it. And that's fine."