Hours after a deadly terror attack in Barcelona, President Donald Trump suggested that Islamic terrorists should be executed with bullets soaked in pig’s blood, praising a discredited story of a 20th-century atrocity.

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

The tweet referenced a false story that Trump told at rallies more than once on the campaign trail. Trump claimed that during the Moro rebellion in the Philippines between 1901 and 1913, U.S. Gen. John Pershing executed Muslim insurgents with bullets dipped in pig’s blood. Trump’s retelling of the myth has changed each time

That story has been discredited by historians, some of whom concluded it would have been “out of character” for Pershing. But other accounts of the Philippine conflict have suggested that U.S. troops did use pigs or pig’s blood to threaten or intimidate Muslims in other situations. Muslims consider pig’s blood to be unholy and ingesting pork to be a sin.

“So yes, there were deliberate efforts to offend Muslim Filipinos’ religious sensibilities,” Christopher Capozzola, a history professor at Massachusetts Institute of Technology, told TIME last year. “And yes, there was large-scale violence against their communities. But I know of no event like the one that Mr. Trump describes.”

Earlier in the day, Trump condemned the attack in Barcelona, which police are treating as an act of terrorism. At least 12 people were killed and 80 were injured when a van plowed into a crowd in the Spanish city.

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Write to Katie Reilly at Katie.Reilly@time.com.