It may be a deterrent, but what would NATO do if Russia invaded anyway knowing that any conventional military response by NATO would be very, very difficult. Would we [and the other NATO members} be willing to go to nuclear war to defend Georgia?
In the unlikely scenario that Russia would invade a NATO member state, I think we would respond with conventional means, and win.
We’ve reserved the first-strike doctrine, so it remains as an option. But it’s highly unlikely that we would be the first to use nukes.