But the White House must recognize that the game has already changed. U.S. credibility is on the line. For all the temptation to hide behind the decision to invade Iraq based on faulty intelligence about weapons of mass destruction, Obama must realize the tremendous damage he will do to the United States and to his legacy if he fails to act. He should understand the deep and lasting damage done when the gap between words and deeds becomes too great to ignore, when those who wield power are exposed as not saying what they mean or meaning what they say.

The distrust, cynicism and hatred with which the United States is regarded in much of the world, particularly among Muslims across the Middle East and North Africa, is already a cancer. Standing by while Assad gasses his people will guarantee that, whatever else Obama may achieve, he will be remembered as a president who proclaimed a new beginning with the Muslim world but presided over a deadly chapter in the same old story.

The world does not see the complex calculations inside the White House — the difficulty of achieving any positive outcomes in Syria even with intervention, the possible harm to Obama’s domestic agenda if he plunges into the morass of another conflict in the Middle East. The world would see Syrian civilians rolling on the ground, foaming at the mouth, dying by the thousands while the United States stands by.