Not if history is any guide. James Fearon finds that nations typically get less aggressive after obtaining nuclear arms:

Obviously the fact that the other members of the nuclear club generally didn’t get much more aggressive in their foreign policy behavior after they tested doesn’t mean that Iran won’t.  But I think it’s astonishing how weak a case for this we are hearing from the preventive war advocates like Kroenig, or politicians contemplating it like Ehud Barak as reported in the Times article.  … We’ve heard these same concerns before, regarding Stalin’s USSR, Mao’s China, Kim Jong-il’s North Korea, and about the mortal mutual enemies of India and Pakistan.  All these cases have been very scary, and it’s understandable that the prospect of a nuclear Iran is incredibly scary for Israelis.  But so far, in none of these prior cases do the more extreme fears look historically justified.