Thomas E. Ricks reports... Pentagon insiders say that he rubbed civilian officials the wrong way -- not because he went all "mad dog," which is his public image, and the view at the White House, but rather because he pushed the civilians so hard on considering the second- and third-order consequences of military action against Iran... Like, what do you do with Iran once the nuclear issue is resolved and it remains a foe? What do you do if Iran then develops conventional capabilities that could make it hazardous for U.S. Navy ships to operate in the Persian Gulf? He kept saying, "And then what?" ...Mattis and Obama differed on Iran. "A particular point of disagreement was what to do about mischief Iran is exporting to other countries. Mattis is indeed more hawkish on this than the White House was," ... "National Security Advisor Tom Donilon in particular was irked by Mattis's insistence on being heard. I cringe when I hear about civilians shutting down strategic discussions. That is exactly what the Bush administration did in late 2002 when generals persisted in questioning whether it was wise to invade Iraq. That led to what some might call a fiasco."
General Officers tend to have weak spines. Those who went along with LBJ on Vietnam, for instance.