It’s a shame that Russia and China won’t go along — but their calculations are so transparently cynical that their refusal has no moral force. Their reflexive noncooperation merely weakens the conflicting international-law norm. In this case, their objections should be disdained and dismissed.
Yet you can’t dismiss the lack of support among U.S. allies or among U.S. citizens. If the U.K. isn’t willing to join airstrikes against Assad, that in itself undermines the chemical-weapons taboo. The same would be true for punitive attacks that weren’t supported in the U.S. Congress or across the country. Remember, the aim isn’t just to damage Assad militarily, which the U.S. could do without allies or congressional approval, but to express a moral consensus. If that consensus turns out not to exist — or if it exists in theory but is spineless in practice — the case for action falters. We’ll have discovered that the taboo against chemical weapons was so much posturing.
Obama says he’s made his decision and has the right to act regardless of what Congress decides. Striking Syria even if Congress says no would be a remarkable gamble. It would also be less potent (because the norm would have been eroded in any event) and on balance unwise. Does that mean he was wrong to ask for authorization? Again, no. The more backing Obama can muster, the stronger the affirmation — and that’s what counts.