But what should an officer do who knows from years of training and combat experience that the coalition the president is assembling cannot accomplish its goals without U.S. combat troops? Does the officer swallow his reservations?…

Senior officers must accept their commander in chief’s judgment and carry out orders. But they and like-minded advisers have another option: resigning. Not to embarrass the administration or cause a constitutional crisis, but to indicate the gravity of the ISIS threat. Until stopped, ISIS or its collaborators are likely to mount an attack against the U.S. homeland with the aim of equaling or surpassing al Qaeda’s 9/11 success. A military commander’s resignation, accompanied by a clear and respectful explanation, would prompt a needed debate over U.S. strategy to achieve the president’s goal “to degrade and ultimately destroy” ISIS.

Resigning on principle is not a strong tradition in the U.S. military. The so-called Revolt of the Admirals in the late 1940s began with the resignation of Navy Secretary John L. Sullivan following Defense Secretary Louis Johnson’s cancellation of the carrier U.S.S. United States. The argument over the carrier was a dispute over budget cuts and the combat roles of the Navy and Air Force. And the naval officers whose careers ended in the wake of Sullivan’s principled resignation did not jump. They were pushed. But the Truman administration’s defense cuts came with a price that was realized when the president learned that reductions in naval power prevented an effective blockade of North Korea.