The Trump administration and its allies are belatedly coming to grips with the military and economic costs of a war that has proved far more complex than they imagined. But as they continue to pour resources into fighting in the Middle East, they seem not to apprehend another consequence: the effect on their party of yet another failed war, this one waged side by side with Israel. If Kent’s criticism of the war proves prescient, his other beliefs, especially those concerning Jews, will ascend in stature along with it. The most prominent Republicans publicly making a forceful case for foreign-policy restraint are the most bigoted ones. If the war goes pear-shaped, they will be poised to steer the party’s future.