After he won, though, and Democrats attempted to challenge his victory in the key states of Wisconsin, Pennsylvania, and Michigan, Trump reversed his position. In a filing in the Michigan case, his campaign argued that “all available evidence suggests that the 2016 general election was not tainted by fraud or mistake.” Even after winning the election, getting inaugurated president, and arguing in court that voter fraud didn’t affect the outcome of the 2016 election, Trump still can’t let this issue go, suggesting that he’s still bothered by his incomplete victory.

Voter fraud is a ghost-like issue, cyclically raised by politicians to cast doubt on the legitimacy of electoral outcomes. But concerns about voter fraud are not founded in credible evidence. “By any measure, voter fraud is extraordinarily rare,” wrote Justin Levitt in a 2007 Brennan Center report on the issue. Most cases of purported voter fraud actually involve typographical errors or other technical mistakes made by citizens who are eligible to vote, he reported. And the kind of fraud Trump has alleged—that millions of non-citizens voted in 2016—is practically non-existent. As Levitt wrote:

We are not aware of any documented cases in which individual non-citizens have either intentionally registered to vote or voted while knowing that they were ineligible. Given that the penalty (not only criminal prosecution, but deportation) is so severe, and the payoff (one incremental vote) is so minimal for any individual voter, it makes sense that extremely few non-citizens would attempt to vote, knowing that doing so is illegal. Although there are a few recorded examples in which non-citizens have apparently registered or voted, investigators have concluded that they were likely not aware that doing so was improper.

During the press conference on Tuesday, Spicer was most likely referring to a Pew Report published in 2012—it’s one Trump cited on the campaign trail. In that report, Pew’s researchers argued that the voting system is inaccurate, costly, and ineffective, and that voting rolls contain millions of incorrect entries or registrations for dead people. But those are issues with registration; they don’t indicate that invalid votes are actually being cast. Their findings do not support the claim that widespread voter fraud has taken place; after Trump pointed to this report on the campaign trail, one of the report’s authors disagreed on Twitter with the conclusions he’d drawn from it. Trump’s other favorite piece of evidence for widespread voter fraud—an article on a Washington Post blog written by Old Dominion University professors—has widely been debunked.

Trump announced his intentions to open an investigation on Wednesday only after journalists—including NPR’s Mara Liasson and CNN’s Jake Tapper—asked why he had not sought to investigate claims that would amount to the most massive electoral fraud in American electoral history. Spicer hinted that an investigation might be a possibility on Tuesday: When repeatedly pressed by reporters, he said only, “Maybe we will [investigate],” later adding, “let's not prejudge what we may do in the future.”