And if that doesn't do it, don't be surprised if Russia arms these missiles with tactical nukes - Putin has already hinted that it might become necessary to use them. And, IMO, Putin will do what ever it takes to keep Syria from becoming an Islamic state - even if it means the total destruction of Syria (Isaiah 17).
The Russians won't cross this red line. Because it would result in the destruction of the Russian military via nuclear attack. Anything less would mean the dissolution of NATO.