There is no discernible tactical benefit to the U.S. getting involved in Syria. In fact, there is every reason to stay away -- to let two enemies continue their war against each other to the bitter end, then re-evaluate how to engage (or not) whomever emerges. The only good reason for the Americans to get involved is humanitarian.
The Syrian government has now established a permanent network of surveillance over the old city. One night recently I was strolling through the souq and saw a figure walking slowly ahead of me in the poorly-lit passage, an object dangling from their arm. When I drew within a few paces, he started and turned quickly to face me, watching me closely as I passed.