I worry that it's not about one big red button but gradual escalation. Somebody decides that using tactical kiloton Nukes is the way to go and other side would

I worry that it's not about one big red button but gradual escalation. Somebody decides that using tactical kiloton Nukes is the way to go and other side would not dare escalate further. A lot of people think if they do the big fearsome escalation, then the other side will back off. Everything up to this point indicates this is Putin's logic. He may be over committed now - what option other than finishing invasion does he realistically have that preserves any goals or prerogatives? In some ways the rational thing, from his perspective, is to keep escalating until other side acts "rationally" and backs off. It's all a giant game of chicken, and I am not convinced that all state leaders anywhere let alone everywhere are rational and fearful enough.