The world will not see this as prudence but rather as dithering — reinforcing the perception that the United States is hiding behind its economic woes and, hounded by the ghosts of Iraq, is no longer keen on leading the world. That will embolden America’s adversaries and deject its friends. America could soon find itself alone in standing up to Iran or North Korea, or in pushing back against China and Russia, which have used their veto power on the Security Council to block United Nations authorization for intervention in Syria.

Americans are justifiably weary of war, but the lesson of Syria is that shirking from our global responsibilities will only create bigger problems that will eventually raise both the cost and the likelihood of American intervention.

Given the impasse at the United Nations, and with Turkey and France the only allies publicly supporting an American-led intervention, Mr. Obama’s desire to seek the blessing of Congress (even though he maintains he does not legally need it) is understandable. But waiting for lawmakers to return from their summer recess to respond to an international crisis sends the wrong message to the world.