Volume rising in Trump’s nativist talk. Southwest rises as 2018 Senate battleground.

WASHINGTON — Despite ongoing rebukes over his defense of white supremacists, President Donald 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, Trump recalled a debunked event in which Gen. John 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 a van was driven into a busy tourist boulevard, killing 13.

“Study what Gen. Pershing of the United States did to terrorists when caught,” 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, 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.

Trump also appeared in peril of losing support from key Republicans he will need to advance his agenda in Congress. Sen. Bob Corker, the chairman of the Foreign Relations Committee, questioned the president’s “stability,” and Sen. Tim Scott, the only black Republican in the Senate, declared Trump’s moral authority is “compromised.”

Corker, a sober voice on foreign policy and a frequent ally of the Trump administration, bluntly questioned the president’s ability to perform the duties of his office.

“The president has not yet been able to demonstrate the stability, nor some of the competence that he needs to demonstrate in order to be successful,” Corker told reporters. He said Trump had not “appropriately spoken to the nation” about Charlottesville, Va.

Scott, R-S.C., insisted that he would not “defend the indefensible” when it came to the president’s comments about “both sides” in Charlottesville being responsible for Saturday’s violence.

“What we want to see from our president is clarity and moral authority,” Scott said in an interview with Vice. “And that moral authority is compromised when Tuesday happens — there’s no question about that,” he said, noting the president’s remarks in which he criticized the “alt-left” while abandoning condemnations of the Ku Klux Klan and neo-Nazis.

Earlier Thursday, Trump made clear he has no intention of stepping back from his assertions about the Charlottesville rally that have drawn widespread condemnation. In three tweets, Trump defended Civil War-era statues, using language very similar to that of white supremacists to argue the statues should remain in place.

On Twitter, Trump called it “foolish” to remove statues of Robert E. Lee and Stonewall Jackson and mused that monuments to George Washington and Thomas Jefferson would be next. “Sad to see the history and culture of our great country being ripped apart with the removal of our beautiful statues and monuments,” the president wrote.

And as he faced a new round of bipartisan denunciations, Trump also lashed out at two senior Republican senators who have been unsparing in their criticism, accusing Sen. Lindsey Graham, R-S.C., of “publicity seeking” and calling Sen. Jeff Flake, R-Ariz., “toxic” and “WEAK.

The White House announced that Trump had decided to cancel plans to assemble a President’s Advisory Council on Infrastructure. The decision to abandon the business group came a day after a revolt among industry leaders on two other advisory panels forced the president to disband them.

Meanwhile, Carmen de Lavallade, a dancer and choreographer who will be honored by the Kennedy Center in December, announced that she will forgo the reception at the White House.

Even so, White House officials said Trump was in good spirits Thursday as he continued a working vacation at his estate in Bedminster, N.J.

Within his administration, his chief of staff, John F. Kelly, was said to be deeply frustrated and unsure how to contain his boss.