MOMENTS after John Kerry concluded a deal with Sergy Lavrov, his Russian counterpart, to destroy Syria's chemical weapons, Barack Obama restated his line that "if diplomacy fails, the United States remains prepared to act". For any number of reasons the deal may yet prove unworkable. In as little as a week, if Syria does not follow through on the requirement to fully account for its chemical arsenal, Bashar Assad could face punitive action from the United Nations. But since Russia continues to object to the use of military force, Mr Obama may eventually find himself back in the bind he was in last week, deciding whether to act without the blessing of the United Nations Security Council (not to mention Congress). Mr Obama has claimed international legitimacy for a potential strike by pointing to the norm against the possession and use of chemical weapons, which is codified in the Geneva Protocol and the Chemical Weapons Convention. His administration has also cited the Kosovo war as precedent for non-UN-approved humanitarian intervention conducted through an international coalition. Russia and China, the two members of the Security Council standing in the way of an attack on Syria, both vetoed a resolution to approve the use of force in Kosovo in 1999. Bill Clinton responded by ignoring the UN, rallying a NATO coalition and waging a 78-day air assault to protect Kosovars.

There are a host of differences between the Kosovo war and the present situation in Syria. But Mr Obama’s decision to thumb his nose at the UN—members of his team have said the Security Council is a “disgrace”—is indeed reminiscent of Mr Clinton’s decision 14 years ago, and of Mr Obama’s decision in 2011 to join in an air campaign on Libya without explicit UN authorisation. "I'm comfortable going forward without the approval of a United Nations Security Council that, so far, has been completely paralysed and unwilling to hold [Syrian President Bashar] Assad accountable", Mr Obama said in August.

Is Mr Obama right to disparage and possibly circumvent the UN? On one hand, failing to take action against a recalcitrant Syria is to permit an international norm against chemical warfare to go unpunished. On the other hand, bombing Syria without UN approval is a violation of the UN Charter; it is itself a breach of international law. So, if the Russian plan to remove chemical weapons from Syria falters, international law will go unvindicated in one way or another.

One way to look at it is through the prism of moral hazard. If Mr Assad were allowed to get away with gassing his own people and failing to keep his promise to turn over his arsenal, Syria and other nations would have little to deter them from flouting the UN and using chemical weapons in the future.

But if America ignores the Security Council now, other nations may be tempted to bypass it later. This is the concern Jack Balkin, a law professor at Yale, aired at the Atlantic:

The whole point of the charter is to prevent member states from attacking each other based on their individual interpretations of international law. If Russia or China decided to attack an American ally on the grounds that it had violated international law, the United States would surely object, and rightly so. Even if America’s goal is humanitarian intervention with the purest of motives, it would be legal under the charter only if the Security Council determined that humanitarian intervention was justified. What Obama is proposing to do is precisely what the charter was designed to prevent.

The problem with Mr Balkin's argument is that it is at least a decade too late. Walter Russell Mead correctly pronounced the UN a “study in failure” last year:

The reality is that the UN today is less prestigious and influential than it was in the 1940s and 1950s. There used to be a time when General Assembly votes actually meant something. Newspapers used to report its resolutions on the front page. And the Security Council, on those rare occasions during the Cold War when it could actually agree on something, was seen as laying down the basic principles along which an issue would be resolved. The increasing feebleness of the UN reflects several developments. The first is experience; as more and more actors figure out how toothless it is and how little its resolutions actually matter, more and more governments simply ignore it. And as that happens, it looks even more toothless, and even more governments conclude that they don’t have to worry much about it.

The bombing of Syria would merely be the latest example of the UN being ignored. "In Syria," says Mr Mead, "arriving UN ceasefire monitors are greeted with artillery barrages. Iran continues to ignore resolutions on opening its nuclear facilities to inspectors. And North Korea merrily flouts UN resolutions as it fires rockets and tests nukes pretty much at will." An American military mission against Syria would carry a moral justification these examples lack. If he were to flout the UN and attack Syria over Russian and Chinese vetoes, Mr Obama would be acting to punish Mr Assad for violating a global rule against deploying chemical weapons. He would be violating a rather weakly respected international norm in order to sustain a more pressing norm. The UN, meanwhile, would remain about as powerful as it has been in recent years. Which is to say, not very powerful at all.