When Putin says he is not bluffing, then he usually is, except when he isn’t. Thus he can threaten to use X, and make movements to use X, and watch to see how such intel is leaking to the West, but it might also get the West to set off a pre-emotive strike, at which point they will have successfully swapped moral high ground, and Putin can declare with perfectly dry feet that he never truly intended to push said red knob.