I might sound cynical,. but I think Trump's decision to strike Syria was more based on his flagging popularity than moral outrage over gassing civilians.  He needed a deflection from both his failures and the gaffes of his administration.  

It's sad but true that any time an American president initiates a military strike his popularity goes up.  And it's no secret that Bannon relishes the idea of armed conflict.

So what is Justin to do?  Damascus needs a hard lesson, but if Trump escalates the attacks he will be between a rock and a hard place.  We can't really afford to antagonize the elephant we sleep with, but armed conflict is in direct contrast to sunny ways and diplomacy.  I see the Russian connection more as a problem for Trump, but that will have to factor into the decision as well.

Could the Security Council step in and chart an acceptable course?  Not bloody likely.  Yer on yer own, Justin....except for Gerald, of course.