Your including the OIR link actually undermined your own argument in several ways. First, it was a non-state actor. Second, that non-state actor had recently, and was actively plotting continued acts of military aggression against US targets. You could even argue a defacto state of war existed, due to their hostile acts. Not even the strictest Constitutionalist has ever argued that an Exec needed Congressional approval to shoot back. Though some have argued that Congress should have issued official letters of marque and reprisal against nonstate actors.

Assad has no history of, and no known current hostile intent against the USA, and is thought to pose no threat at all. There's a huge world of difference between attacking neutral state actors, and actively hostile nonstate actors.

For who could be free when every other man's humour might domineer over him? - John Locke (2nd Treatise, sect 57)