If the AP report is true, this is a complete win for the President:
Assad is now agreeing to preserve and strengthen that norm. He’s agreeing to sign the treaty banning chemical weapons — a treaty Syria has been one of the lone holdouts against. He’s creating a situation in which it would be almost impossible for him to use chemical weapons in the future, as doing so would break his promises to the global community, invite an immediate American response, and embarrass Russia.
This is, in many ways, a better outcome than the White House could have hoped for. Punishing Syria may or may not have actually reinforced the norm against chemical weapons — particularly if the strikes went bad and the American people punished members of Congress who voted for them. But Syria joining the treaty against chemical weapons definitely, almost definitionally, reinforces the ban.
This we call "diplomacy." And it's good to see when it works.