That's the problem with the Middle east. Every time the West tries to make a terrible situation better, we make it a whole lot worse.
It seems to be an impossible situation. 
Yes it is, and it has all the ingredients of causing a major world conflict. We should never appease evil, but we should fully understand what is at stake if "we" go in with boots on the ground. The USA will do what they want to do under Trump, but any action should be under the flag of the UN. That is what the UN is
meant to be for, although really it is a toothless organisation, as international law is toothless, without the support of the US.
But it is clear that action must be taken against any country committing war crimes, so doing nothing should not be an option. Once more it will come down to us all taking the lead from the US and going in or not with them as I cannot see any credible Arab alternative; they just have not got the will or hardware, with those like Saudi Arabia who maybe could make a difference tied up with existing war demands on their own military.
So, here we go again, the World is being tested by a rogue state, but one that is led by someone who is not after regional / world domination, so do we want to risk a conflict with Russia over this? So, time for Trump to talk to Putin and combine to rid the World of Assad, solving a "local" problem without making this bigger than it has to be. This is not Czechoslovakia of 1938 or Poland of 1939, so we must not over react.
