President Donald Trump’s suggestion for North Carolina voters to cast their ballots twice in the upcoming presidential election stirred fears of voter fraud, with critics quick to point out the illegality of double voting.

The ongoing coronavirus pandemic almost certainly will prompt a number of voters across the country to submit absentee ballots by mail. But the president, looking to solidify his chances in key battleground states like North Carolina, said voters should also show up in-person on Election Day come Nov. 3.

“They are going to have to check their vote by going to the poll and voting that way because if it tabulates, then they won’t be able to do that,” Trump said to reporters on Wednesday. “So let them send it in, and let them go vote. And if their system is as good as they say it is, then obviously they won’t be able to vote. If it isn’t tabulated, they will be able to vote.”

The president doubled down on his claims, without evidence, at a rally in Latrobe, Penn. the following day. “You have to make sure your vote counts, because the only way they’re gonna beat us is by doing that kind of stuff,” he told the crowd.

In the wake of Trump’s comments in North Carolina, the state’s Attorney General Josh Stein tweeted that the president “outrageously encouraged [North Carolinians] to break the law in order to help him sow chaos in our election.”

It is a federal crime to vote twice in the same election, in addition to being outlawed in 31 states and Washington, D.C. Experts say so-called “double voting” in rare in modern elections in the United States, but it still can happen.

A recent analysis of state records by the Cincinnati Enquirer found that 2,177 Ohioans total attempted to vote twice in the past three presidential elections. The number, however, represented just 0.013% of the more than 17 million ballots cast, illustrating the move’s rarity. The paper added that each one of these extra votes were flagged by election officials and eventually discarded.

A March 2020 study by researchers from Stanford, the University of Pennsylvania, Harvard, and Microsoft, noted that despite double voting being “one of the most common assertions of voter fraud,” it’s difficult to identify instances due to public restriction of voter information, such as social security numbers.

Ultimately, the study concluded that double voting “is not currently carried out in such a systematic way that it presents a threat to the integrity of American elections.” The researchers estimated that, at most, one in every 4,000 votes cast in 2012 were double votes.

Still, it’s important to note that the study was published before the scope of the coronavirus pandemic’s impact on the election became clear, and the likely record numbers of mail-in votes that will occur as a result. Seeking to limit the spread of misinformation, both Facebook and Twitter posted warning labels over Trump’s posts urging his supporters to vote by mail and then follow up in person. “Voting by mail has a long history of trustworthiness in the US and the same is predicted this year,” said a message accompanying Trump’s post on Facebook.

As for the Democrats, they accused Trump of attempting to undermine the legitimacy of the election.

“Let’s be clear,” said Reyna Walters-Morgan, the Democratic National Committee’s director of voter protection, “voting by mail is a safe and secure way for Americans to participate in our democracy—and Trump should be working to make it easier to vote, not harder.”