Joshua Roberts / Reuters

The president is tweeting again.

Three weeks into a government shutdown triggered when the president reneged on a deal to fund the government, insisting instead that any deal had to include money for a wall on the southern border, Donald Trump tweeted about a story from the Washington Examiner that cited an anonymous rancher who claimed that Muslim “prayer rugs” were found at the U.S. border. Although the president likely imagines that this strengthens the case for his border wall, it’s really just an example of how the president will say anything he thinks backs him up, regardless of whether it’s true.

“There’s a lot of people coming in not just from Mexico … People, the general public, just don’t get the terrorist threats of that,” the story quotes the rancher as saying. “That’s what’s really scary. You don’t know what’s coming across. We’ve found prayer rugs out here. It’s unreal. It’s not just Mexican nationals that are coming across.”

That is the entirety of the evidence provided for the discovery of “prayer rugs” at the border. The Examiner provides no photographs, no press accounts, no confirmation from government documents or sources—just the word of a single anonymous rancher. The same rancher also warns that the Border Patrol has caught migrants of other nationalities, including “Czechoslovakians.” Czechoslovakia hasn’t existed since George H. W. Bush was president. It’s one thing to use anonymous sources; it’s another to print whatever they say without a cursory attempt at verification.

As it happens, the claim that prayer rugs prove that terrorists have infiltrated the southern border is something of an urban legend, akin to the stories about a kid who ate Mentos and drank Diet Coke and exploded. In 2014, the right-wing website Breitbart mistook an Adidas T-shirt for a prayer rug; David Dewhurst, a former Republican lieutenant governor of Texas, repeatedly told audiences that prayer rugs were found at the border. As Vox’s Matthew Yglesias noted, finding prayer rugs at the border was also a plot point in the action film Sicario: Day of the Soldado, which was released last year.

Even if the claim were true, it would prove nothing. It can provoke alarm only on the basis of the bigoted assumption that every Muslim is a terrorist, and therefore the presence of a prayer rug somewhere along the U.S.-Mexico border means that terrorists have sneaked into the United States. You can buy prayer rugs to decorate your home with on Etsy; you can also use them in devotions. It is an absurd and prejudiced assumption that they are an indication of terrorism, rooted in nothing more than animus toward Muslims. It is bad enough that some Americans provide an eager audience for this kind of nonsense. It is catastrophic that one of them is president.

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