re: the "last resort" aspect
I agree that it should, and probably would, be used as a last resort by pretty much anybody. Even Iran. But, let's think about what that can mean.
Hypothetical scenario: We are fighting Iran. We are kicking their butts. They know they're going to lose, and lose bad. At that point, they may literally believe that they have nothing left to lose, and throw some nukes our way as a "last resort".
It's not just a "last resort" aspect from our point-of-view, but from the other side's point-of-view also.