Let the folks with all the information handle it.
Iran will start it. We expect them to.
If the UN doesn't impose sanctions, there will still be some type of sanctions without UN approval. Iran has said if sanctioned they will act as if they are at war with the West, because sanctions are an act of war.
Once they start the actual war, whether overt, conventional military action or terrorism or both, President Bush knows that he must respond to it. He has no choice.
And he will say, we tried diplomatic means until we ran out of them, and the world will see that he is correct.
Whether they want to admit it or not...