Although Assad has all but won the civil war in Syria, he has yet to win the peace: As last weekend's chemical attacks illustrate, the country remains a humanitarian disaster.
In deciding how to retaliate, the U.S. must recognize that a symbolic response will be hollow if not accompanied by a more robust strategy. Even at this late stage, there is still an obligation for the international community to intervene purposefully.
The bottom line: Assad must be contained. Russia has given indispensable support to his regime against a largely unsupported opposition and extremist militias with limited armament. But a joint U.S.–NATO intervention would change the equation, and having Putin on his side won't help him if the action is swift and thorough.