Somewhere in my reading today I ran across a brief mention that Gens. Kelly and Mattis found themselves opposing Gen. McMaster on some issues--it seems the split was between those who tried to rein Trump in (Kelly-Mattis) versus McMaster who was more willing to go along.
I can't wait for McMaster's memoir. If I recall his dissertation, converted into a well-regarded history called Dereliction of Duty, was critical of LBJ's Joint Chiefs for not being straight with him, for going along with his policies rather than resisting the expansion of the war without being open with the public. So if today's item was correct, it might be that McMaster found it hard to play the role of adviser than he thought it was back in his academic and youthful days. Wouldn't be the first, nor will it be the last, person to make the discovery.
[Update: it was a New Yorker piece: "On one side were Mattis, Tillerson, and Kelly, each of whom in varying degrees sought to push back against the President; on the other was McMaster, who made his natural allies furious for what they saw as his habit of trying to accommodate the President’s demands, even if they were far-fetched. “General McMaster was trying to find a way to try to execute, not to tell him no,” the former government official told me."