Here's the conundrum as I see it.
Defeat Assad and ISIS fills the vacuum.
Do nothing and Assad butchers innocent people.
The one line that I think should never be crossed is chemical weapons. My opinion is that requires a swift and harsh response at all times. Having said that however, I don't think Trump has really done anything to address the chemical weapons. He informed Russia, who's allied with Assad, about the attack well ahead of time. What exactly did they do to incapacitate Assad? Nothing.
But hey, at least Donnie can pretend Putin doesn't have him on a leash. Right?
"Look how mad Putin is at me, guys! I'm not his lackey!"