President Donald Trump called for an investigation into illegal voting that he says took place in the 2016 presidential election, despite no evidence that widespread voter fraud ever occurred.

I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states, those who are illegal and.... — Donald J. Trump (@realDonaldTrump) January 25, 2017

even, those registered to vote who are dead (and many for a long time). Depending on results, we will strengthen up voting procedures! — Donald J. Trump (@realDonaldTrump) January 25, 2017

Trump told congressional leaders on Monday that “3 to 5 million” undocumented immigrants cost him the popular vote by casting ballots for Hillary Clinton, according to HuffPost sources. And White House spokesman Sean Spicer confirmed on Tuesday that Trump actually believes this, citing two recent studies.

But NBC looked into those studies and found that one had been widely debunked. The other, from Pew, “found millions of out of date registration records due to people moving or dying, but found no evidence that voter fraud resulted,” the report’s author explained.

Democrats were quick to denounce Trump’s efforts to delegitimize the November vote, but Republicans― with a few exceptions― have shied away from outwardly denouncing his lies.

This won’t be the first time the federal government has investigated reported instances of voter fraud. Under President George W. Bush, the Department of Justice conducted a five-year probe into what critics at the time called an attempt at suppressing votes from Democrats. According to the New York Times, the investigation turned up “no evidence of any organized effort to skew federal elections.” When people were arrested for voter fraud, it was largely due to clerical errors in registration or confusions about eligibility.

Samuel Levine contributed reporting.