If Iran decides to play with the big boys, then it has accepted that responsibility. For better or worse, this is their choice.
A "first strike" nuclear attack from America is justified and would be the wisest choice.
A "first strike" nuclear attack from America is justified
Doctrine for Joint Nuclear Operations
"Executing a nuclear option, or even a portion of an option, should send a clear signal of United States' resolve. Hence, options must be selected very carefully and deliberately so that the attack can help ensure the adversary recognizes the "signal" and should therefore not assume the United States has escalated to general nuclear war, although that perception cannot be guaranteed."