Donald Trump is already coming up with excuses for a potential loss on Election Day.

On Fox News, he said on Tuesday that the election is part of “a rigged system,” arguing that “there are reports that when people vote for Republicans, the entire ticket switches over to Democrat.”

There are credible reports of some voting machines malfunctioning, although not in the way that Trump described or due to a vast conspiracy — instead, the machines sometimes just don’t work correctly for all sorts of reasons, including user error. In fact, so far there are no credible allegations of voter fraud on Election Day.

But Fox News didn’t fact-check him, instead going into a question about how he would feel if he lost.

To be clear, voter fraud is extremely rare. For example, Loyola Law School professor Justin Levitt has tracked credible allegations of in-person voter impersonation for years, finding 35 total credible allegations between 2000 and 2014, when more than 800 million ballots were cast in national general elections and hundreds of millions more were cast in primary, municipal, special, and other elections.

There are other kinds of potential voter fraud, such as vote buying, insider ballot box stuffing, double voting, and voting by people who turn out to be ineligible. But all of these are also extremely rare, and there’s no evidence that they have swung national elections, according to experts (and even Breitbart, a pro-Trump outlet).

This isn’t the first time Trump has complained about voter fraud. As the polls have consistently shown him behind, Trump has increasingly stepped up his rhetoric about the “rigged” election. But there’s no evidence to back him up.