Donald Trump posted a tweet in the immediate aftermath of the Barcelona attack that suggested people should study a famed US general who was said - incorrectly - to have suppressed Muslim militants by shooting them with bullets dipped in pigs' blood.
Mr Trump initially posted a message of support in which he condemned the attacks. Then he said people should look at the history of an early 20th Century general, John Pershing. He appeared to be referring to a widely debunked story that Pershing overcame militant Muslims in the Philippines by killing them and burying their bodies with pigs.
Another part of the legend is that he killed them with bullets dipped in pigs' blood.
Both narratives have been proven false by historians who have studied Pershing's activities in the Moro province from 1909 to 1913. The claims were not verified in Pershing's memoir and did not fit his documented behaviour, according to Politifact.
Also, "the idea that pig’s blood could serve as a weapon against Muslims has been around in popular culture for decades," according to Polifact.
Mr Trump has made the claim before, notably in February 2016 during the Republican primaries.
Mr Trump tweeted 15 minutes after he sent a message of support to the people of Barcelona via his personal Twitter account.
It seems to suggest that the President is assuming the attackers - two people have been arrested so far - are Islamist terrorists and that his preferred method for dealing with them is pigs' blood bullets, or threatening to bury them with pigs.
He has not tweeted a clarification nor have any White House spokespeople spoken on the matter.
The terror group Isis has claimed responsibility for the attack, but that claim has not been confirmed by the authorities.
