With attention on recount efforts in several swing states, President-elect Donald Trump late Sunday claimed, without proof, that “millions of people…voted illegally.”

Trump wrote on Twitter that “serious voter fraud in Virginia, New Hampshire, and California” cost him the popular vote, though current tabulations estimate that Democratic nominee Hillary Clinton is ahead by nearly 2 million votes.

During the rant, Trump argues that his campaign strategy of visiting many small states would have made it “much easier” for him to “win the so-called popular vote than the Electoral College,” where he is currently ahead of Clinton 290-232.

“There’s no reason to believe this is true,” said Rick Hasen, blogger at the Election Law Blog and professor specializing in election law at the University of California, Irvine.

“The level of fraud in U.S. elections is quite low,” Hasen noted, adding that, in particular, “the problem of non-citizen voting is quite small—like we’re talking claims in the dozens, we’re not talking voting in the millions, or the thousands, or even the hundred.”

Fact-checking website Politifact also ruled Trump’s assertion false.