WASHINGTON — Despite ongoing rebukes over his defense of white supremacists, President Trump defiantly returned to his campaign’s nativist themes on Thursday. He lamented an assault on American “culture,” revived a bogus, century-old story about killing Muslim extremists and attacked Republicans with a renewed vigor.

Hours after a terrorist attack in Spain, Mr. Trump recalled a debunked event in which Gen. John J. “Black Jack” Pershing supposedly killed Muslim rebels in the Philippines by shooting them with bullets dipped in the blood of pigs, which Muslims are forbidden to eat. The Islamic State claimed responsibility for the attack in Barcelona, where the driver of a van crashed into a busy tourist boulevard, killing 13.

“Study what General Pershing of the United States did to terrorists when caught,” Mr. Trump tweeted, spreading a mythical story even as he again accused the news media of being “Fake News” in another tweet. “There was no more Radical Islamic Terror for 35 years!”

As when he trafficked in the same unproven legend during the presidential campaign, Mr. Trump ignored the conclusions of historians, who repeatedly have said it did not happen. Additionally, his claim that Pershing ended terrorism in the Philippines for 35 years is refuted by the violence that continued for decades after the rebellion that ended in 1913.