Stephen M. Walt is Robert and Renee Belfer professor of international affairs at Harvard University. He blogs at Foreign Policy magazine and is on Twitter.

Even if proven, the use of chemical weapons by the Syrian government does not tip the balance in favor of U.S. military intervention. To think otherwise places undue weight on the weapons Assad’s forces may have used and ignores the many reasons that U.S. intervention is still unwise.

Of course it is not good that Assad's forces may have used chemical weapons, but it is not obvious why the choice of weaponry changes the calculus of U.S. interests in this case. The brutal nature of the Assad regime has been apparent for decades, and its forces have already killed thousands with conventional means. Does it really matter whether Assad is killing his opponents using 500-pound bombs, mortar shells, cluster munitions, machine guns, icepicks or sarin gas? Dead is dead, no matter how it is done.

The brutal nature of the Assad regime has been apparent for decades, and its forces have already killed thousands with conventional means.

Proponents of action argue that the U.S. must intervene to defend the norm against chemical weapons. Using nerve agents like sarin is illegal under international law, but they are not true “weapons of mass destruction.” Because they are hard to use in most battlefield situations, chemical weapons are usually less lethal than non-taboo weapons like high explosive. Ironically we would therefore be defending a norm against weapons that are less deadly than the bombs we would use if we intervene. This justification would also be more convincing if the U.S. government had not ignored international law whenever it got in the way of something Washington wanted to do.

And intervention is still a bad idea. Airstrikes cannot eliminate Assad’s chemical arsenal and are unlikely to tip the balance in favor of the rebels. And even if they did, this situation would give Assad a bigger incentive to use these weapons more widely. Assad’s fall would create a failed state and unleash a bitter struggle among the various rebel factions. The Syrian uprising may have started as a peaceful reform effort, but today the most powerful rebel groups are jihadi extremists, the last people we want in power in Damascus. These prudential concerns still apply, regardless of the weaponry Assad's forces may have employed.

Lastly, Obama may be tempted to strike because he foolishly drew a “red line” over this issue and feels his credibility is now at stake. But following one foolish step with another will not restore that lost standing. U.S. power is most credible when it is used to protect vital U.S. interests. The United States has little interest in getting bogged down in Syria, and the use of chemical weapons by Syrian government forces does not alter that fact.