Other than some statements from his Press Secretary there will be no reaction.
Ultimately, its a very tough call for us. There is no clear 'good' guy in this fight. Both the government and rebels have committed war crimes, both stand for governments we would eventually come to hate, and really, both sides probably wont like us once they enter into power. Its an incredibly tough situation diplomatically, but I think we really cant do much at this point, as awful as that feels.
Air strikes against sites in which the poison gas is manufactured or stored?