From what I have read and heard about Gen. Mattis is that he is anything but a 'warmonger'. Most of his quotes in the press are single sentences totally devoid of place, time and context, and merely reflect lazy journalistic practices, at best. He appears to be a well and widely read scholar, and, more importantly, very much his own man. I suspect he would have little issue with advising the Commander in Chief of his shortcomings, and certainly not via Twitter. I think he could be an excellent choice.