[amalter]

I disagree. I believe the intentions would start as a non-nuclear response, but would rapidly spill out of control into a full send of all weapons.

This is the reality of the "Assured Destruction" of MAD. If you can take out your enemies ability to respond you can "win". With a tactical nuke in play and Rus-vs-US force engagement moves us to DEFCON 1. The name of that level is "COCKED PISTOL". A cocked pistol is something to handle gently, any wrong nudge could set it off.

Then in the background you have air to air engagements over the Black Sea - blockades of Kaliningrad, SSN's chasing SSBN's. Dozens of Cuban Missile Crisis type situations all playing out in parallel. One bad call by one local commander and a head of state is given 6 minutes to figure out if this is a first strike.

Once the line is crossed almost all of us die. It might take hours, days or weeks - but it will be an near inevitable conclusion.