Blustering like that tells me that the Ukraine invasion is very probable. It's the only reason he would make such a geopolitically inflammatory statement like that. He wants to create deterrence to any intervention at all making evyerone fear escalation. It may or may not be a bluff but why would anyone use nukes???
“.....why would anyone use nukes???”
Remember Saddam Husain retreating when he thought all was lost and burning up his oil fields (the future) in the process?
Try backing a bear into a corner and all you have is bear spray. Any clue what will happen next?
Rational thinking can disappear in a heartbeat. That’s why the cold war lasted for 50 years (MAD). Our current leaders think MAD is something that happens to you when someone stands up to your foolish demands.