Ironic, given the GOP still control the House of Representatives; I guess it's a catch-22 for them, either they stop Obama going to war (thus defeating Obama) and risk the argument that they failed the Syrians, or they have to tacitly accept Obama going to war.
I think it is fair that Congress have to justify going to war really, though there are risks in that sort of system. I'm sure Obama doesn't really want to go to war if he can help it; too much of his base of support was always about cheapening/getting out of big ground conflicts of the Iraq & Afghanistan type.