I'm not even certain it wasn't war-gaming an invasion of the Baltics. But the outcome at the time, apparently, was no nuclear response. This was controversial due to NATO's defence pact.
Anyway, as regards the current situation, I think most of us can agree that what Putin has done is abominable. Where I think there is room for more debate is in the response. Many people in the West who abhor Putin will be asking themselves: "how involved do we really need to get in this?"
I mean, speaking for myself, are we really going to risk nuclear destruction for Ukraine? This is the bitter realpolitik of things. I am not saying we should or we shouldn't. I am simply saying that this is the question. There are no easy answers to this. If we do risk it, we had better be absolutely and definitively correct in our judgement that we will not be fried. If we don't risk it, are we sacrificing the Ukrainians? Are we saying: there is a line, but it is only at NATO/EU borders? Ukraine, it seems to me, is the horrible victim of its geography. The idea that Ukraine will have some "total victory" is for the birds. Unless the Putin regime somehow collapses in on itself, I can't see how that could ever happen. At some point, there is going to have to be negotiations and bitter concessions. When that is, who knows? The Ukrainians have every right to defend themselves. But this is dangerous for the rest of us, too. Horrible times.