I think there is a major difference between chemical weapons and bombs that can be used for terrorist attacks versus nuclear ICBMs. One thing is to invade a country that can use chlorine gas against our troops, but placing the existence of our country and possibly humanity on the line is another thing entirely. Iraq could have potentially used gas attacks against it’s population, allied populations and troops. However, Russia could nuke the hell out of NATO and cause a catastrophic worldwide famine for decades.