Someone comes to kill you, kill them first. הקם להרגך הקדם להרגו. This is straight forward principle from the Talmud. You don't wait until they have shot at you. You shoot them immediately when their intention is clear. I should mention this right to self defense applies to Jews also. They don't need to wait until they are nuked in order to take action.

Since Iran announces their intention to wipe Israel off the map and they say every day in their radio programs exactly what they are planning on doing with the Bomb there is no need to wait until their fulfill their desires.