President Donald Trump just can’t stop talking about voter fraud. In a closed-door meeting with senators on Thursday, participants told Politico that Trump ranted as former New Hampshire Sen. Kelly Ayotte was in the room about how she would have won her reelection in November if “thousands” of people weren’t “brought in on buses” from Massachusetts to New Hampshire to vote “illegally.”

Like other Trump conspiracy theories about voter fraud, there is zero evidence for his claim. But this isn’t the first time Trump has made these kinds of claims in front of members of Congress, previously telling congressional leaders, the Associated Press reported, that “he would have won the popular vote in the 2016 election if 3 million to 5 million immigrants living in the country illegally hadn’t voted.”

All of that followed months of comments by Trump — as a candidate for president, as president-elect, and now as president — about voter fraud. “In addition to winning the Electoral College in a landslide,” he tweeted in November, “I won the popular vote if you deduct the millions of people who voted illegally.”

The comments appeared to culminate late in January when, in a series of tweets, Trump announced that he would launch an investigation into voter fraud. But that investigation has yet to be officially unveiled.

Trump’s main source for his claims is an old Pew report, whose authors have repeatedly said that it does not support Trump’s claim at all. It doesn’t even look at voter fraud, but rather at America’s lackluster technology for registering voters.

More broadly, respected research on voter fraud has found again and again that it’s extremely rare in the US. At most, there might be a few hundred fraudulent votes in national elections — in which well over 100 million people can vote.

“The claim that there were millions of illegal voters in this past election is false and unsupported by any credible evidence,” Rick Hasen, a professor of law and political science at the University of California Irvine, wrote. “The National Association of Secretaries of State, made up of the chief election officers of all 50 states, just issued a statement saying so.”

Still, Republicans have pushed the myth of widespread voter fraud for years — to justify new voting restrictions — as a political tactic: Depressed voter turnout almost always favors the GOP by hitting disproportionately Democratic demographics, making new hurdles to voting attractive to Republican politicians. And Trump, similarly, could use his investigation into voter fraud to justify new national restrictions on voting.

“A shoddy investigation could be a pretext for imposing new laws making it harder for people, especially people likely to vote for Democrats, to register and vote,” Hasen told me.

So while it’s easy to dismiss Trump’s doubling, tripling, and quadrupling down on this myth as bluster, it can have real consequences — consequences that reach into the most basic, fundamental right that American citizens share.

The research is clear: Voter fraud is rare to nonexistent

There have been multiple investigations — by academics, journalists, and nonpartisan think tanks — into voter fraud. None found evidence of anything close to millions of people voting illegally.

Loyola Law School professor Justin Levitt studied voter impersonation, the type of fraud that strict voter ID laws (which Trump supports) aim to curtail. Levitt found 35 total credible accusations between 2000 and 2014, constituting a few hundred ballots at most. During this 14-year period, 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.

A 2012 investigation by the News21 journalism project looked at all kinds of voter fraud nationwide, including voter impersonation, people voting twice, vote buying, absentee fraud, and voter intimidation. It confirmed that voter impersonation was extremely rare, with just 10 credible cases.

But the other types of fraud weren’t common either: In total, the project uncovered 2,068 alleged election fraud cases from 2000 through part of 2012, covering a time span when more than 620 million votes were cast in national general elections alone. That represents about 0.000003 alleged cases of fraud for every vote cast, and 344 fraud cases per national general election, in each of which between 80 million and 135 million people voted. The number of fraudulent votes was a drop in the bucket.

What’s more, not all — maybe not even half — of these alleged fraud cases were credible, News21 found: “Of reported election-fraud allegations in the database whose resolution could be determined, 46 percent resulted in acquittals, dropped charges or decisions not to bring charges.”

Trump and his team, in his defense, have cited a 2012 report from the Pew Center on the States as evidence for their claim. But the report didn’t even focus on voter fraud. Instead, it looked the technical aspects of voter registration systems, and how America could save money by upgrading how it registers voters.

As part of that, the Pew report found that more than 1.8 million registered voters were actually dead, while 2.75 million had registrations in more than one state. This is where Trump apparently got his “millions” figure.

But that doesn’t mean that even one of these registrations was used for illegal votes. America has a multi-step system for voting: You register, then vote. The report only shows that people registered and were never taken off the rolls. They didn’t even have to register for the latest election — some of them registered for the 2008 election, then died or moved, and states just didn’t take them off their rolls. So someone could have simply registered in Ohio in 2008, moved to Pennsylvania by 2012, and simply forgotten to notify Ohio’s elections system that he had moved — even though he never had any intention of voting in Ohio again.

For example, Steve Bannon, Trump’s chief strategist and senior counselor, reportedly voted for Trump in New York. But it turns out that he was also still registered to vote in Florida last year, because he never officially deregistered in the Sunshine State, even though he didn’t vote there.

And David Becker, who worked on the 2012 Pew report, unequivocally said that the report found “zero evidence of fraud.”

That doesn’t mean voter fraud has never happened and never had an impact. The New York Times, for instance, reported on a 1997 case in which it was revealed that Miami Mayor Xavier Suárez clinched his electoral victory “with the help of hundreds of absentee ballots bearing the names of dead people, felons and other ineligible voters.” While Suárez was never charged, he was eventually forced to step down from office after an appellate court threw out the absentee ballots.

But this type of situation, the empirical evidence and experts suggest, is likely far too rare to swing much bigger elections. When debating whether to do something about voter fraud, then, it’s important to consider whether the potential downsides — such as making it harder for people of color to vote or sowing doubt in US elections — are worth the upside of stopping a tiny number of fraudulent votes. Otherwise, you might get prominent politicians like Trump casting doubt on the entire electoral process.

The voter fraud myth has been used repeatedly to suppress voters

It would be one thing if this were just a ridiculous myth that the president was shouting into Twitter. But this exact myth of widespread voter fraud has repeatedly led to actual changes in law and policy.

Notably, Trump isn’t the first Republican, or even Republican presidential candidate, to raise concerns about voter fraud.

In 2008, many Republicans and conservative media outlets like Fox News promoted fears that ACORN — a community organization that focused in part on registering African-American voters — was engaging in mass-scale election fraud. At the time, Republican nominee John McCain warned that ACORN “is now on the verge of maybe perpetrating one of the greatest frauds in voter history in this country, maybe destroying the fabric of democracy.” (Again, there was zero evidence of this, and it did not happen.)

And the myth that undocumented immigrants in particular are voting illegally has been promoted for years by right-wing conspiracy websites like Infowars — citing a highly criticized 2014 report, even though one of its authors has said it didn’t find proof of widespread voter fraud.

Touting these kinds of concerns, 14 states passed new voting restrictions — from strict photo ID requirements to limits on early voting — that were in place for the 2016 election: Alabama, Arizona, Indiana, Kansas, Mississippi, Nebraska, New Hampshire, Ohio, Rhode Island, South Carolina, Tennessee, Texas, Virginia, and Wisconsin. Other states passed restrictions, but they’re currently tied up in court battles.

Republican leaders have also embraced other tactics that limit people’s ability to vote, including purging voter rolls, going after voter registration groups, and closing down polling places. These efforts were all emboldened by a 2013 Supreme Court ruling that weakened the Voting Rights Act, which banned discrimination at the voting booth, by limiting federal oversight of changes certain states make to their voting laws.

States’ measures typically target voter impersonation. They require a certain kind of ID to vote — Texas, for example, allows government-issued IDs (including concealed gun permits) but not student IDs. This, obviously, makes it much harder for someone to impersonate another voter.

But states’ voting restrictions can also take other steps that don’t seem to target fraud so much as make voting more difficult. North Carolina’s law, for example, also eliminated some early voting days, ended same-day voter registration and out-of-precinct voting, and stopped the preregistration of 16- and 17-year-olds in the state.

Republicans, who tend to push for these laws at the state level, nonetheless insist that their goal is to limit voter fraud. And for years, they have echoed rhetoric like McCain’s and Trump’s to convince people that voter fraud really is a big problem that requires burdensome laws to fix.

A previous report by the US Department of Justice captured the sentiment among many Republicans: Rep.﻿ Sue Burmeister, a lead sponsor of Georgia’s voter restriction law, told the Justice Department that "if there are fewer black voters because of this bill, it will only be because there is less opportunity for fraud. [Burmeister] said that when black voters in her black precincts are not paid to vote, they do not go to the polls." Other Republicans, such as former North Carolina Gov. Pat McCrory and Iowa Rep. Steve King, have similarly warned about the dangers of voter fraud.

So as much as Trump is a political aberration in many respects, he really isn’t out of line with the typical Republican rhetoric on voter fraud. Still, that doesn’t diminish the very real consequences of his rhetoric.

Trump’s investigation could be a pathway to national voting restrictions

Not only could Trump’s words cast doubt on the entire electoral system in the US — a system that relies largely on people believing that it’s fair — but Trump could use the claims and his federal investigation, potentially led by the US Department of Justice, to justify a crackdown.

An investigation could do some good. Hasen notes that if it, like past investigations into election issues in 2000, 2004, and 2008, takes a nonpartisan approach with a commission of election experts from both political parties, it could help get to the bottom of all of these issues and finally put them to rest. But he cautioned that “there is no reason to believe that any investigation Trump orders would be fair and a search for the truth.” (For one, the White House later said that the investigation will focus on the bigger states that Trump lost — suggesting a vendetta of sorts.)

Levitt of Loyola Law School agreed, arguing that Trump’s investigation seems more about looking for facts that prove his argument rather than getting to the truth of the matter. “Normally I have more confidence in the integrity of an investigation that doesn’t announce the conclusion before the investigation starts,” he said. “It sure looks like there’s an answer that there’s now to be an investigation to find the facts for.”

For example, if the investigation finds, like the 2012 Pew report did, that there are millions of outdated voter registrations, Trump and Republicans could stretch that finding to justify a national voter ID law or mass purge of the voter rolls.

When states have done the latter, it’s led to many legitimate voters losing access to the ballot without any notification, simply because they didn’t update their addresses or didn’t read their mail, or officials used faulty databases for their purges.

And if Trump wants to pursue a massive voter purge, he could, citing his fear of undocumented immigrants voting, use an existing federal database for it: the Systematic Alien Verification for Entitlements database (SAVE), which is used to identify immigrants eligible for social services.

States like Colorado, Florida, Iowa, and North Carolina have tried to use SAVE in the past for voter purges. But the Obama administration warned that the database wasn’t designed for it and could mistakenly flag immigrants who’d since become US citizens — which is exactly what happened. The result: Potentially thousands of people were wrongly removed from the voter rolls — and many more could be wrongly removed if Trump takes a similar path.

This is the kind of problem that advocacy groups are worried about in the coming days.

“The President swore to uphold the Constitution just five days ago. That includes the right to vote. That is what the highest officials in the land should preserve, protect, and defend. The stakes for democracy couldn’t be higher,” Brennan Center for Justice president Michael Waldman said in a statement. “There is no evidence of massive voter fraud — none. The notion that millions of people voted illegally two months ago, and nobody noticed, is preposterous on its face. Election officials, leaders of the President’s own party, and every academic and journalistic investigation confirm this.”

And based on the evidence, minority voters — who are, conveniently for Trump, more likely to vote Democrat — would very likely suffer the worst of these consequences.

Voter fraud fears can lead to racist consequences

Republican-backed voting restrictions don’t affect everyone equally. Time and time again, the evidence has shown that they tend to keep eligible minority voters in particular from casting a ballot — and Republicans have at times admitted that this was their intent.

Some studies suggest voter ID laws make it particularly harder for black and brown Americans to vote. One widely cited 2006 study by the Brennan Center found voter ID laws, for instance, disproportionately impacted eligible black voters: 25 percent of black voting-age citizens did not have a government-issued photo ID, compared with 8 percent of white voting-age citizens. And a study for the Black Youth Project, which analyzed 2012 voting data for people ages 18 to 29, found 72.9 percent of young black voters and 60.8 percent of young Hispanic voters were asked for IDs to vote, compared with 50.8 percent of young white voters.

One reason for these kinds of numbers is disparate enforcement — polling officials, perhaps driven by racial biases, appear more likely to ask minority voters for an ID.

But minority voters are also generally hit harder by voter ID laws and other restrictions on voting. For example, since minority Americans are less likely to have flexible work hours or own cars, they might have a harder time affording a voter ID or getting to the right place (typically a DMV or BMV office) to obtain a voter ID, rely more on early voting opportunities to cast a ballot, or require a nearby voting place instead of one that’s a drive, instead of a walk, away from home or work.

For civil rights groups, the restrictions call back to the days of poll taxes, literacy tests, and other rules that were imposed to block minorities from voting until the Voting Rights Act effectively banned such laws. Like modern voting restrictions, the old laws didn’t appear to racially discriminate at face value — but due to selective enforcement and socioeconomic disparities, they disproportionately kept out black voters.

Again, minority voters tend to lean Democratic. So Republicans are effectively making it harder for the other party’s voters to vote.

Some Republicans have even admitted that this is the goal of the new wave of voting restrictions. As William Wan reported for the Washington Post:

Longtime Republican consultant Carter Wrenn, a fixture in North Carolina politics, said the GOP’s voter fraud argument is nothing more than an excuse. "Of course it’s political. Why else would you do it?" he said, explaining that Republicans, like any political party, want to protect their majority. While GOP lawmakers might have passed the law to suppress some voters, Wrenn said, that does not mean it was racist. "Look, if African Americans voted overwhelmingly Republican, they would have kept early voting right where it was," Wrenn said. "It wasn’t about discriminating against African Americans. They just ended up in the middle of it because they vote Democrat."

The US Department of Justice is supposed to act as a check on these kinds of voter suppression efforts. But under Republican administrations, the agency has approached voting rights cases with a lack of serious interest — with the Bush administration in particular known for effectively treating civil rights enforcement as a joke.

With Trump’s nomination of Attorney General Jeff Sessions, who has opposed key parts of the Voting Rights Act throughout his career, the Trump administration looks poised to take a careless approach. In fact, it might even set aside resources toward supporting states’ voter suppression efforts by dedicating time and money to investigating and cracking down on voter fraud — exactly what Trump is now suggesting.

Now, the research shows that voter ID laws and other voting restrictions have a fairly small overall impact on elections, at most reducing turnout by a percentage point or two.

But even if voting restrictions don’t have a big effect on the ultimate outcome of elections, they still appear to disproportionately keep minority voters from exercising their most basic democratic right — a problem no matter how you slice it. And it’s a problem that’s perpetuated through a total myth: a false claim that there’s a lot of voter fraud in America when the evidence simply shows otherwise.

Watch: It’s now on America’s institutions — and Republicans — to check Donald Trump