This does not, of course, amount to blanket permission for self-destructive military actions such as attacking China or surrendering to Monaco. But the course Obama contemplates does not fall into such a category. What has been dismissed as “therapeutic bombing” would actually be a military response to the violation of an important international norm. Not every gesture is an empty gesture. And even if this military action were wrong or pointless, it would have to be sufficiently dangerous to justify the gelding of the executive branch on a global stage.

A limited military strike may be symbolic. But for Congress to block that strike would be more than symbolic. It would undermine a tangible element of American influence: the perception that the commander in chief is fully in command.

The refusal to authorize force would be taken as an ideological pivot point. Nations such as China, Russia and Iran would see this as the triumph of a political coalition between the peace party of the left and the rising isolationists of the right. And they would be correct. The strategic calculations of every American enemy and friend would be adjusted in ways that encourage challenge and instability. Prime Minister David Cameron’s recent loss of the vote authorizing military action — the first such repudiation since 1782 — has weakened Britain as an actor in the world. America should refuse to follow it down.