Richard Price, author of the The Chemical Weapons Taboo, discusses how strikes against Syria might affect it:

Bombing Syria would be the strongest possible upholding and reinforcement of the norm. Will the norm fall by the wayside if that doesn’t happen? No, I don’t think it will. But if there was a strike to enforce it, that would be a watershed moment in many respects. Norms regarding warfare have often been quite effective, like the treatment of prisoners of war. They’re sometimes violated, of course, but a lot of them are treated with a minimal level of decency. These norms trudge on, despite violations, because of beliefs about reciprocity and decency. One violation does not destroy a norm. What matters is how people respond to it.

And you’ll notice something strange about this episode. It’s not as if Syria is defending their use of chemical weapons. They’re denying it. And that helps contribute to the notion this is an unacceptable process. In World War I, the Germans argued that gas might be more humane than bayonets or getting blown up. Some people think that the Bush administration’s view on enhanced interrogation techniques struck a real blow against norms against torture. No one is defending chemical warfare. All the dynamics here have served to highlight that this is a salient norm in global politics today.

Here, again, we keep ignoring what the Bush administration did. They tore up international norms. They made it clear that they had nothing but contempt for them. They occupied a country and failed to provide minimal security for its citizens thereafter, a violation of Geneva. They authorized and practiced grotesque torture of prisoners. They showed contempt for allies. They went to war without full UN permission. They established a torture-and-detention camp in no-man’s and in Cuba precisely to flout international norms.

The idea that America is the only thing standing between chaos and international norms simply ignores the entire history of this rogue, sole super-power in the first decade of the 21st Century. Obama had a chance to restore those norms, but on torture, he simply refused to uphold very clear Geneva imperatives that torturers and their commanders be prosecuted for war crimes. So to take Price’s point:

One violation does not destroy a norm. What matters is how people respond to it.

We know how Obama has responded to it. By doing nothing. Torture is as grave a violation of international law as the use of chemical weapons. I fail to see why a president who refuses to enforce international norms against torture in his own country has any right to tell anyone else on the planet what they can and cannot do in observance of international norms. He has trashed them in the case of torture for domestic political reasons. Why shouldn’t Assad – when he is facing a fight for survival?

We have, in other words, not a leg to stand on when we claim we are enforcing international norms. We only enforce them when we want to. (On chemical weapons, we actively allowed Saddam to use them when it suited us.) In any case, I don’t see how this Syrian adventure will do anything serious to reinforce those norms, as Isaac Chotiner notes:

Does anyone think if Saudi Arabia, say, develops and uses chemical weapons to put down a revolt a decade from now that the United States would go to war? Of course not. (Hypocrisy is not a reason to avoid action, but massive hypocrisy does mean the messages and signals a country thinks it is sending tend to be muddled.) It’s possible that regimes we dislike will hesitate before using these weapons, although that too seems unlikely if those regimes face an existential threat. The possible benefit—i.e. the range of possible bad actors that would be dissuaded by a limited war in Syria—seems awfully small.

Drum argues that most supporters and opponents of war with Syria aren’t focused on chemical weapons:

Enforcing a century-old ban against the use of chemical weapons may sound high-minded in the abstract, but down on the ground there’s virtually no one who (a) actually cares about that and (b) would view a U.S. strike through that lens. You’re for it because you’re a Democrat or a Sunni or an Israeli or a member of the rebel army. You’re against it if you’re a Republican or a Shiite or an Egyptian or Vladimir Putin. Hardly anyone truly cares about American credibility or international norms or foreign policy doctrines or any of the other usual talking points. They’ve just chosen sides, that’s all.