At first glance, the twists and turns of Mr. Obama's Syria policy made the president seem indecisive, if not incoherent: calling for Mr. Assad to step down without taking direct action against him, even after the regime's use of chemical weapons in defiance of Mr. Obama's "red line"; attacking the jihadists of the Islamic State while allies like Turkey and Qatar supported other extremist groups; opposing Russian designs and then coordinating airstrikes with Moscow.