Christopher Miller, director of the National Counterterrorism Center, will replace Mark Esper as acting secretary of Defense, President Trump tweeted on Monday. Why it matters: Trump has clashed with Esper over a number of issues since the summer, and he was expected to be one of the first Cabinet secretaries to be removed after the election.Between the lines: The Pentagon chief lost Trump's favor after he rebuffed the idea of sending active-duty military to deal with racial justice protests over the summer and distanced himself from the clearing of Lafayette Square protesters for a photo op at St. John's church.Esper has also been working with Congress on legislation to remove the names of Confederate leaders from military bases, a move that has further put him at odds with the president, according to NBC News.The change is effective immediately. Miller previously oversaw special operations forces in counterterrorism.The big picture: Other Cabinet officials expected to be fired by Trump in the lame-duck session include CIA Director Gina Haspel and FBI Director Christopher Wray. Trump has also teased the idea of firing Anthony Fauci, but he would not be able to do so directly because Fauci is not a political appointee. What they're saying: "I am pleased to announce that Christopher C. Miller, the highly respected Director of the National Counterterrorism Center (unanimously confirmed by the Senate), will be Acting Secretary of Defense, effective immediately," Trump tweeted."Chris will do a GREAT job! Mark Esper has been terminated. I would like to thank him for his service."In an interview with the Military Times on Nov. 4, Esper — realizing that he was on his way out — pushed back on the notion that he was a "yes man" for the president.“My frustration is I sit here and say, ‘Hm, 18 Cabinet members. Who’s pushed back more than anybody?’ Name another Cabinet secretary that’s pushed back,” Esper said. "Have you seen me on a stage saying, ‘Under the exceptional leadership of blah-blah-blah, we have blah-blah-blah-blah?’"“At the end of the day, it’s as I said — you’ve got to pick your fights. I could have a fight over anything, and I could make it a big fight, and I could live with that — why? Who’s going to come in behind me? It’s going to be a real ‘yes man.’ And then God help us.”