By EILEEN SULLIVAN and MICHAEL D. SHEAR
WASHINGTON — Stephen Miller was furious — again.
The architect of President Trump’s immigration agenda, Mr. Miller was presiding last month over a meeting in the White House Situation Room when he demanded to know why the administration officials gathered there were taking so long to carry out his plans.
A regulation to deny welfare benefits to immigrants — a change Mr. Miller repeatedly predicted would be “transformative” — was still plodding through the approval process after more than two years, he complained. So were the new rules that would overturn court-ordered protections for migrant children. They were still not finished, he added, berating Ronald D. Vitiello, the acting head of Immigration and Customs Enforcement.
“You ought to be working on this regulation all day every day,” he shouted, as recounted by two participants at the meeting. “It should be the first thought you have when you wake up. And it should be the last thought you have before you go to bed. And sometimes you shouldn’t go to bed.”
A few weeks after that meeting, the consequences of Mr. Miller’s frustration and the president he was channeling have played out in striking fashion.
Mr. Trump has withdrawn Mr. Vitiello’s nomination to permanently lead ICE and pushed out Kirstjen Nielsen, his homeland security secretary. The department’s acting deputy secretary, Claire Grady, and the Secret Service director, Randolph D. Alles, are departing as well. And the White House has made it clear that others, including L. Francis Cissna, the head of United States Citizenship and Immigration Services, and John Mitnick, the department’s general counsel, are likely to go soon.
Mr. Trump insisted in a tweet on Saturday that he was “not frustrated” by the situation at the border, where for months he has said there is a crisis that threatens the nation’s security. But unable to deliver on his central promise of the 2016 campaign, he has targeted his administration’s highest-ranking immigration officials.
And behind that purge is Mr. Miller, the 33-year-old White House senior adviser. While immigration is the issue that has dominated Mr. Trump’s time in office, the president has little interest or understanding about how to turn his gut instincts into reality. So it is Mr. Miller, a fierce ideologue who was a congressional spokesman before joining the Trump campaign, who has shaped policy, infuriated civil liberties groups and provoked a bitter struggle within the…