Love to know Israel's response too the S-300 & 400. And despite Obama's prickly relationship with Bibi and Israel, did they share their counter too these weapons w/ BHO....
If they have a counter, they're not going to show their hand until there's something worth letting the Russians know they have the counter; i.e. against something much more important than targets in Syria that can be attacked by artillery or commandos.
If the US were to begin air-strikes my bet is they'd first let the US go in without whatever they've worked out for themselves which then makes any effective counter they may have worth a lot more if the US is foiled, and if the US has no problems, lets them know they don't need to share whatever they have until it becomes worth more to the US.
JMHo based on past history