This is what eventually will happen, but over Putin's dead body most likely. "Live by the sword, die by the sword", that kinda thing, etc. Everybody agrees that by starting this pointless war Putin has painted himself into a corner.
ie. there are still diplomatic ways out of this open to Putin. If he is not open to considering them and feels cornered, it is his own shortsightedness and failing.
It has been said that you should never draw your pistol unless you are going to shoot. I don't know if that's true; but I do think it's unwise to threaten violence unless you are quite sure you are prepared to carry through.
I think Putin is prepared to carry through (he's made the threat more than once). Russia seems to be losing in Ukraine; but they can't be seen to be slinking away with their tail between their legs. So I think there's a good chance Russia will pop a tactical nuke in Ukraine.
For the same reasons, NATO can't be seen to tolerate the popping of tactical nukes in a regional conflict; they would have to retaliate, for fear that their nuclear deterrent be treated as a joke. I haven't any idea how NATO might select their target, though; striking a city would be gross over-reaction, and striking Russians in Ukraine would be rather counterproductive.
NATO should definitely not respond to nukes with nukes unless Putin drops one on a NATO country. Ukraine is not in NATO. That makes it a first strike, not a retaliatory strike. Putin's propaganda has been that NATO is an aggressor threatening Russia. If NATO strikes Russia in retaliation for a strike on a non-member country that only vindicates him, and you know, leads directly to WWIII
Hey, I didn't mean to sound like a cheerleader for global thermonuclear war! I'm just observing that the logic of nuclear deterrence calls for a response whoever Russia attacks. If it becomes clear that Russia can nuke anyone it likes as long as they're not in NATO, then it can march into e.g. Georgia or Armenia with a company of conscripts, and take over, declaring that any resistance will be met with nukes.
Suppose Russia pops a small nuke in Ukraine? Really, that's not going to achieve any major military victory. They'd need a few to end the war in Russia's favour. That would result in clouds of fallout afflicting NATO countries. At some point you'd have to say "that's enough". But at what point? After two? A dozen? Only after the first megaton city-flattener?
I was a member of CND for a year, back in the 80's. I still favour unilateral disarmament. I quit not because I didn't support the goals, but because I was shocked at the political infighting I observed at the Annual General Meeting.
Not everybody. The "NATO pushed Putin into corner by inviting Ukraine" theorem is still alive. In any way, cornered Putin is angry Putin and angry Putin is dangerous and may be unpredictable.
Do you of a good source that covers the topic?
You can use Realism to predict that Russia would eventually try to regain the power it lost over Eastern Europe and the Baltics with the dissolution of the USSR. In fact that very understanding and fear is precisely why countries in Eastern Europe and the Baltics pushed so hard to join NATO and the EU, because they predicted that would happen.
But that doesn't make Russia's actions the right move, either legally or morally. They have agency too and could always have made the choice to not to try to act like an empire with violent hegemony over their neighbours.
2. "NATO pushed..." does not imply Russia is right. Russia is wrong, legally and morally, but it can be simultaneously true that NATO pushed Russia.
2. "NATO pushed" is deceptive framing. The countries that joined NATO after 1991 had to lobby hard over many years to get NATO members to agree to expand. Even then the process took forever with MAPs and other interim steps each designed to slow the process down.
No wonder China is gleefully standing by. They're just biding their time. When 2 dogs fight over a bone...
Putin has said that Ukraine is a historical mistake, and laments the dissolution of the Soviet union. This war is because he want's to create a larger Russian empire, not a preemptive strike for self defense.