You're walking along the streets at night. A mugger comes out from his hiding place. He points his gun at you and pulls the trigger while you desperately reach for your own gun. His gun misfires.
Do you give him time to pull the trigger again? Or do you blow him away first?
With an Iranian dud first strike, do you assume they don't have more, or do you eliminate the threat right now, with everything you have available?
Blow him away first.