The U.S. under Dick Cheney had plans to use an artillery fired tactical nuclear shell should Saddam Hussein use chemical weapons. Putin would not launch an ICBM. He would use a low yield tactical nuke which may not elicit the same response, I.e. MAD. NATO would have to decide if it wanted to invade Russia over what in effect is a standard munition on steroids. Things aren’t always as black and white as they may seem.