I think he should have supported the more secular democratic elements against the regime. The regime was on the brink of falling and the outcome was probably going to have been not different than where we ended up. Instead Obama stood aside and let Assad and the Russians crush the opposition.

But that's just my opinion. My point being that "let's not intervene and let it play out" ended up with an amazingly bad outcome because the fear of a bad outcome from an intervention. Clearly a bad decision. A good decision, whatever that might have been, would have a better outcome. If the argument is that no better outcome was possible then that seems pretty wrong on the face of it.

Syria, Iraq and Afghanistan (e.g.) are fairly different places.