WASHINGTON — The White House has engaged in a slow-motion purge of hard-line officials at the National Security Council in recent weeks, angering conservatives who complain that the foreign policy establishment is reasserting itself over a president who had promised a new course.

The latest to go was Ezra Cohen-Watnick, who ran the N.S.C.’s intelligence division and, like others who have left, was originally appointed by Michael T. Flynn, President Trump’s first national security adviser. Mr. Flynn resigned in February after it was disclosed that he misled Vice President Mike Pence and others about a telephone call with Russia’s ambassador.

Lt. Gen. H. R. McMaster succeeded Mr. Flynn and has slowly tried to move out some of Mr. Flynn’s appointees. He initially tried to fire Mr. Cohen-Watnick earlier this year, only to be rebuffed by Stephen K. Bannon, the president’s chief strategist, and Jared Kushner, the president’s son-in-law and senior adviser. But Mr. Kushner dropped his opposition this week, according to someone with knowledge of the decision.

A fierce Trump loyalist, Mr. Cohen-Watnick drew attention when he and another White House official briefed Representative Devin Nunes, Republican of California and the chairman of the House Intelligence Committee, on classified intelligence reports revealing that American intelligence agencies had conducted incidental surveillance of Mr. Trump’s transition team. The briefing was intended to bolster Mr. Trump’s unsubstantiated claim that President Barack Obama ordered phones tapped at Trump Tower.