Saturday night, President Donald Trump held a rally in Melbourne, Florida, where he attempted to defend his controversial “Muslim ban” executive order by pointing to the consequences of migration in Europe. He focused on an unspecified event that took place “last night in Sweden”:

When you look at what’s happening in Germany, when you look at what’s happening last night in Sweden — Sweden! Who would believe this? Sweden! They took in large numbers, they’re having problems like they never thought possible.

The only problem is that nothing happened the prior night in Sweden. The Swedish daily Aftonbladet quickly compiled a list of noteworthy things that happened on Friday; They included a drunken-driving arrest and “some technical problems” during 87-year-old crooner Owe Thörnqvist’s rehearsal prior to the Melodifestivalen song competition.

It seemed like Trump, in the grand tradition of the “Bowling Green massacre,” simply invented a terrorist attack allegedly committed by immigrants out of whole cloth.

The reaction was swift and confused. @Sweden, a national Twitter account run by a different Swedish citizen each week, denied that anything happened. Former Swedish Prime Minister Carl Bildt tweeted, “Sweden? Terror attack? What has he been smoking?” Ikea and Abba jokes flew fast and furious using the hashtag #SwedenIncident:

Millions are suffering from free healthcare, superb education, well-engineered cars, and awesome meatballs. #PrayForSweden #swedenincident — Rev. Dr. J. Liam Fox (@JmsWmFox) February 19, 2017

Jokes aside, though, there’s a very real question going on here: What on earth was the president of the United States talking about? What does he think is going on in Sweden?

Our best guess: Sweden’s alleged “rape epidemic”

If you spend any time in the conservative media, particularly alt-right or anti-Islam sites, there’s a clear narrative about Sweden: Muslim migrants are raping Swedish women at unprecedented numbers.

Look, for example, at Breitbart — Trump senior strategist Steve Bannon’s old publication. It’s published an enormous number of pieces in recent years on the alleged migrant rape crisis in Sweden, focusing on cities like Malmö with large Muslim immigrant populations. Representative headlines include “Police warn of child rape epidemic in migrant-occupied Malmo” and “Migrants jailed after woman abducted at gun point, gang-raped in hookah bar basement.”

Breitbart is hardly alone. Virginia Dare, an alt-right site focusing on immigration, published a piece on “Sweden’s ‘refugee’ sexual assault disaster.” Pamela Geller, a widely read anti-Muslim blogger who once published a piece alleging that Barack Obama was the love child of Malcolm X, wrote a piece titled “Sweden Crumbling: Demands for military intervention as thugs turn Malmo into ‘no-go zone.’”

These claims have even made it into more mainstream outlets like National Review and Fox News. Friday night, Fox’s Tucker Carlson interviewed Ami Horowitz, a journalist who said that “from the onset of the refugee crisis, there was a surge in [Swedish] gun violence and rape.” Slate’s Daniel Politi theorizes that Trump watched the segment and hence decided to say something about Sweden in his subsequent speech.

That’s hard to say for sure. But the odds are, given the consistency of the narrative about Sweden in the right-wing mediasphere, that Trump heard one of these claims about a Swedish refugee rape epidemic somewhere — and appropriated them to justify his travel ban.

The problem, though, is that this “rape epidemic” is as fake as the Bowling Green massacre.

Canadian reporter Doug Saunders rigorously investigated the narrative, and concluded that it “falls apart as soon as you speak to anyone knowledgeable in Sweden.” Official Swedish statistics do indeed show a high rate of rape, but that’s because Swedish law has an extremely expansive definition of what qualifies as rape under the law. Sweden has a higher official rape rate, in short, because its police are better able to investigate and prosecute sexual violence.

“What we’re hearing is a very, very extreme exaggeration based on a few isolated events, and the claim that it’s related to immigration is more or less not true at all,” Jerzy Sarnecki, a criminologist at Stockholm University, told Saunders.

These panics about immigration, instead, reflect a long history of sexual panics in the West about nonwhite immigrants. Scholars Selda Dagistanli and Kiran Grewal argue that warnings about an immigrant rape epidemic draw more on preexisting Western prejudices about the violent sexuality of Muslim men than they represent a reaction to actual facts. The so-called “rape epidemic” is just something anti-immigrant campaigners have latched onto to justify their preexisting desire to shut the door on Muslim migration.

So while Trump’s “last night in Sweden” slip-up is pretty funny, it’s likely drawing on a pretty troubling narrative.