The lack of an organizing principle encourages the consideration of each action on its own merits. Arming America’s Kurdish allies in Iraq, for instance, isn’t the same as arming painstakingly vetted rebels in Syria. As Douglas Ollivant, a senior national security fellow with the New America Foundation, told Politico this week, “No one is concerned about the Kurds losing control of these arms on a large scale. That was a big concern with the Free Syrian Army.” Likewise, there is a clearer case for air-dropping aid to Yazidis besieged by ISIS on Mount Sinjar than for sending American planes to help civilians struggling to survive Syria’s brutal civil war. In the words of New York Times columnist Ross Douthat, “Alongside a stronger moral obligation to act than we had in Syria or Libya, we have a clear enough military objective, a more tested ally in the Kurds and a plausible long-term strategy that could follow from intervening now.” What’s more, the American public has consistently opposed escalated military action in Syria, even after the use of chemical weapons by the Syrian government (Americans are more evenly split on the wisdom of conducting airstrikes against Sunni militants in Iraq).