Get the US out of there! What a screwed up mess with no possible benefit to US involvement.
Stopping the Iranians is one benefit. Iran is on a march to the Med - they are following their historic routes of conquest. Once they take Syria, with with or without Russian partnership, they will move on to Israel and up into Greece and thence into Europe proper.
Stopping Turkey’s march to the next caliphate is another, as well as keeping Turkey from allying with Russia.