Trump refers to inaccurate anecdote about Gen. Pershing The president repeated the story on multiple occasions during the campaign.

 -- In a tweet seemingly responding to the terror attack in Barcelona, Spain, President Donald Trump referenced a factually inaccurate anecdote about combatting Muslim enemies that he often repeated on the campaign trail.

Thirteen people were killed when a van drove through a crowd of pedestrians on a busy street in Spain's second largest city Thursday. ISIS later claimed responsibility for the act that left 100 people injured as well.

"Study what General Pershing of the United States did to terrorists when caught," wrote Trump, less than four hours after the attack. "There was no more Radical Islamic Terror for 35 years!"

The president's post was apparently in reference to a legend about World War I-era Army Gen. John J. Pershing that he first told publicly during a campaign rally in Charleston, South Carolina, in February 2016. According to Trump, Pershing dipped the bullets used to execute Muslim terrorists in pig blood. The Quran prohibits the consumption of pork, which is considered to be "impure."

"They had a terrorism problem and there's a whole thing with swine and pigs and you know the story they don't like them ... and Gen. Pershing was a rough guy and he sits on his horse and he's very astute, like a ramrod. ... And he caught 50 terrorists that did tremendous damage and killed many people ... and he dipped 50 bullets in pig's blood," Trump explained.

"And he had his men load his rifles and he lined up the 50 people, and they shot 49 of those people," he continued. "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, OK? Twenty-five years there wasn't a problem!"

At the time the story was told, Politifact, an organization that fact-checks the claims of politicians, evaluated Trump's tale and concluded it to be "ridiculous." Politifact cited eight historians who not only noted that the evidence for the blood-dipped bullet aspect of the story "is thin," but also that violence and unrest continued in the referenced region in the Philippines for years during and after U.S. involvement.

It is unclear why Trump's original claim of "25 years" without "a problem" increased to "35 years" in his tweet Thursday.

Snopes, an additional fact-checking outlet, similarly rated the story as false. In its analysis, Snopes writes of a 1927 Chicago Daily Tribune story noting Pershing "sprinkled some prisoners with pig's blood," which was ultimately "more powerful than bullets" as a warning before releasing the prisoners, as well of a separate account that "attributed the deed to someone other than Pershing."

At a press conference from Trump Tower in New York Tuesday, the president outlined his stance on adhering to factual information in response to a question about his hesitancy to condemn hate groups following violent protests last weekend in Charlottesville, Virginia.

"It takes a little while to get the facts. You still don’t know the facts. And it's a very, very important process to me," said Trump, continuing, "So I don’t want to go quickly and just make a statement for the sake of making a political statement. I want to know the facts."