At The American Conservative, Daniel Larison examines the exit of Defense Secretary James Mattis, and considers who may replace him. He writes (abridged):
As wrong as Mattis was on a number of foreign policy issues, there is a real danger that his successor could be far worse
Even if Trump doesn’t nominate a Tom Cotton or Lindsey Graham, the next Defense Secretary is very likely to be a yes-man in the mold of Mike Pompeo.
Almost every time that Trump has replaced his top national security officials, he has chosen someone who will flatter and praise him instead of telling him the truth and giving him the best advice.
The next Defense Secretary is less likely to resist Trump’s belligerent tendencies, and he is more likely to indulge the president’s worst impulses.
Just as Pompeo has proven to be a worse Secretary of State than Tillerson, Mattis’ successor will very likely prove to be an inferior Secretary of Defense.
Read more here.