The administration’s working assumption seems to be that the Syrians can’t possibly strike back. Iran purchased 12 Kh-55 Kent cruise missiles from Ukraine in about 2001. The Iranian Meshkat cruise missile is rumored to be a reverse engineered Kent. If this rumor is correct and Iran were to provide the Meshkat to their ally Syria, assuming the missile is any good, it could make life exciting for the 6th Fleet and anyone else in the Eastern Med.
Another option: Israel’s INS Hanit had an encounter with a Hezbollah C802 in ‘06. If the Hezzies have them, so do the Syrians.