Credibility? We still have the largest miltiary budget ih the entire world.
I don't know that conviction is the right word. Pragmatic, perhaps. A measured response. One strategy might be to take out Assad's telecommunications, his air fields, his missle launch sites, his palaces, a few newspaper and television stations, etc. However, it might not be a good idea to strike the chemical plants because if the plant isn't totally obliverated then some of the chemical gases could escape and kill thousands more than Assad did. That wouldn't look good, either.
Lets face it, both sides are bad. To take Assad out (regime change) is almost guarrentee that fundamental extremists will fill the void. I don't think the Russians want the latter to happen. Anyway, I think there is another option and that is to separate Syria into two countries. In a nut shell...
Assad has everything to lose and the rebels have nothing to lose.
Imo, separating Syria into two countries might be Assad's best option simply because its better than nothing which is what he will have if he keeps fighting. Diviidning Syria will at least leave Assad with a country to control albeit much smaller and the rebels who had nothing will also have something. Imo, that option opens the door to diplomatic intervention and solution.