Very interesting and a logic i appreciate, being an economist. The ultimate issue is of course that if you «reverse resolve» all options and you keep the rationality hypothesis, nuclear threat is NEVER credible, hence strangely it would be as if nuclear weapons didn’t exist at all. This brings us to expected loss of outcomes: supposing the loss is infinity if a nuke is dropped, even a VERY LOW probility (low but non zero) assigned to that outcome makes the cost infinite. Hence even the smallest belief in the possibility is enough to deter a rational agent from escalation. So the only way «to really know» is to call Putin’s bluff and actually really send NATO ground troops and NATO airforce to Ukraine… and «see what happens»… and that brings us to the non-zero low probability of a nuke and infinite loss. I doubt strongly that putting NATO «back on the table» IN THEORY would deter Putin. I doubt very much it would have any effect at all on him other than intensification. So when do you «manifest» effectively the theoretical threat of sending NATO troops? At one point, if you are all show and no go, tyrants call your bluff…