SRBMs and MRBMs are a different game. They have different launch signatures and trajectories than ICBMs. They wouldn't necessarily elicit the same sort of nuclear response.
In your scenario, would NATO take Putin's warning at face value and just wait around to see what happens? I doubt it. Why wouldn't Russia use SRBMs for the sort of strike you're describing? It's been done before, many times, my a few nations, in anger. Using an ICBM would provoke a nuclear response- it's doctrine. The potential risk is too great and the potential response likely devastating.
|