A MATTER OF PRINCIPLE: Almost from the beginning of his tenure as President Trump’s defense secretary retired Marine Gen. Jim Mattis faced questions of how he could continue to serve a president who did not share his core values. Particularly his belief in the importance of allies, and an understanding that protecting America’s friends was as much in our interests as theirs.

As Trump ignored Mattis’ advice on issue after issue his position became increasingly untenable. The president’s decision to precipitously pull all U.S. pull troops out of Syria and thereby abandon America’s Kurdish allies was more than he could take.