After departing his post as White House chief strategist last week, Steve Bannon told the Weekly Standard that “the Trump presidency that we fought for, and won, is over.” The clear suggestion is that Mr. Trump’s chance at success had followed Mr. Bannon out the door. Trying to recast his ouster as a personal choice, Mr. Bannon bragged “I can fight better on the outside.” He promised “to crush the opposition,” saying “I built a f— machine at Breitbart.” The former adviser also told a Bloomberg reporter he would be “going to war for Trump against his opponents—on Capitol Hill, in the media, and in corporate America.”

Success might not come so easily. Just as before, one of Mr. Bannon’s principal aims will be replacing the GOP congressional leadership by supporting populist primary challengers. But last year his attempted political hit on House Speaker Paul Ryan—for which he recruited a primary challenger and pummeled the speaker daily through Breitbart news stories—ended with Mr. Ryan winning with 84% of the primary vote. Some “f— machine.”

Mr. Bannon also promised that Breitbart would attack Mr. Trump when he deviates from what Mr. Bannon believes should be the president’s agenda. The website proceeded to do just that after the president’s speech Monday on Afghanistan. A “high-level” Breitbart staffer went so far as to tell Vanity Fair that if Trump deviates from the positions he ran on, Breitbart would help “rally votes for impeachment.”

Mr. Bannon is not the first staffer to believe the White House agenda must mirror his own. But no other aide in memory has had such grandiose or destructive plans for trying to remain in charge after being shown the door.

Mr. Trump is also engaged in the threat-fest against his own party. At an Arizona rally on Tuesday, he excoriated Senate Republicans for failing to replace ObamaCare—rather than expressing confidence that a health-reform bill would pass eventually. The president also dismissed Sen. Jeff Flake—a critic of Mr. Trump who faces re-election in 2018—by saying “no one knows who the hell he is.” Most pointedly, he failed to wish Sen. John McCain a speedy recovery from brain cancer. All superb ways to encourage support from a thin GOP Senate majority.