The idea is gaining ground in some circles that an excessively limited strike against Syrian President Bashar Assad's chemical weapons program would undermine U.S. credibility and interests more than would a decision not to strike. On its face, this argument is appealing: After all the buildup and expressions of moral indignation, supporters of intervention would, of course, feel let down by a weak attack. Assad and his Russian and Iranian backers would no doubt declare that they have once again defeated the great superpower. And the media may fill with questions about the United States' strength and determination.

But even a weak strike is more in line with U.S. interests than a refusal to strike or, worse, congressional action blocking any attack. Not just U.S. credibility but also the will of the Syrian opposition is at stake.

Especially after this lengthy buildup and public debate, Syrian rebels and their supporters would view a U.S. failure to act as abandonment of their cause. In particular, the moderate Syrian opposition, which relies on support from the United States and its allies, would be devastated. These people are the majority of the opposition. The al-Qaida franchises that have no expectation of U.S. aid and other terrorists are estimated to comprise 15 percent to 20 percent of Syria's opposition fighters. So at this moment, inaction is likely to strengthen Assad, Iran, Hezbollah and al-Qaida — and weaken the lone group whose interests coincide with America's at all.