The news out of Barcelona this afternoon is heartbreaking: an apparent terrorist in a van targeted a crowded pedestrian plaza, and according to Spanish officials, the current death toll is 13 people, with dozens more hospitalized. One suspect is already in custody.

It’s against this backdrop that Donald Trump, who says he always wants to have all the “facts” before speaking on any subject, thought it’d be appropriate to highlight one of his favorite stories.

“Study what General Pershing of the United States did to terrorists when caught. There was no more Radical Islamic Terror for 35 years!”

For those who followed Trump’s presidential campaign closely, this is familiar rhetoric. The Republican candidate loved to rile up far-right voters by telling them a myth about General John Pershing. Here, for example, is a Washington Post report from June 2016, following a Trump event in South Carolina.

As the crowd cheered him on, Trump told them about Pershing – “rough guy, rough guy” – who was fighting terrorism in the early 1900s. Trump didn’t say where this happened, but variations of this story online usually state that it happened in the Philippines during the Philippine-American War – part of the island nation’s protracted battle for independence – early in Pershing’s career. “They were having terrorism problems, just like we do,” Trump said. “And he caught 50 terrorists who did tremendous damage and killed many people. And he took the 50 terrorists, and he took 50 men and he dipped 50 bullets in pigs’ blood – you heard that, right? He took 50 bullets, and he dipped them in pigs’ blood. And he had his men load his rifles, and he lined up the 50 people, and they shot 49 of those people. And the 50th person, he said: You go back to your people, and you tell them what happened. And for 25 years, there wasn’t a problem. Okay? Twenty-five years, there wasn’t a problem.”

The more Trump told the story, the more he’d change the details of the myth – in several instances, he said Pershing’s solution stopped terrorism for 42 years, or 35 years, or sometimes 25 years – but ultimately, it doesn’t much matter.

Because the myth isn’t real.

As MSNBC reported in February 2016, the Pershing story “appears to be a hoax spread via email forwards.” There’s no evidence to back the apocryphal tale up, and according to experts in the Philippine conflict, the myth doesn’t even make sense.

But Trump continues to repeat and believe the myth, in part because of his anti-Muslim animus, in part because he’s fond of easy solutions to difficult problems, and in part because he long ago gave up on caring about the difference between fact and fiction. The president likes the hoax; therefore, the hoax must be real.

Even if we put aside Trump’s strained relationship with reality, let’s not lose sight of the underlying point the president is eager to emphasize: in his mind, war crimes and mass executions are effective and worthwhile elements of an effective national security strategy.

He’s dangerously wrong.