Obama’s approach represents a misunderstanding of wartime leadership. It is not possible for a president to justify the use of force by downplaying it. Americans support armed conflict when the stakes are highest, not when the costs are lowest. It is a tribute to their moral seriousness. There is no way for a president to accommodate American war weariness by setting “unbelievably small” goals; he must overcome it by explaining urgent, unavoidable national purposes. If Obama can’t define those purposes in Syria, his wartime leadership will not succeed.

He has a strong moral and strategic case to make. Bashar al-Assad is the author of poison gas attacks against children — the latest in a series of mass atrocities aimed at civilians. Tolerance for such butchery would be a source of historical shame and an invitation to future crimes. But this moral stand is located within a broader strategic argument. A dangerous alliance of Iran, Syria and Hezbollah, with outside support from Russia, is seeking dominance in a region essential to U.S. interests. It is important to prevent their victory in the Syrian civil war and to avoid the destabilization of key allies. And it is necessary to make clear that Iran’s proxy, the Assad regime, cannot use weapons of mass destruction with impunity. For Congress to undercut Obama in his confrontation with Damascus would invite future miscalculations in Tehran.