As one political analyst said today the battle is between a set of monsters (Assad & co) and a set of maniacs (radical muslims) with a glint of moderation in the embattled minority Kurds.
Wading in is likely a worse answer than wringing our hands and doing nothing and why on earth Trump wants to get involved is beyond my understanding.
Edit: Unless of course the game is to see what anti-missile defences the Russians have against the US of A's second tier of missiles.