The best estimates that I have seen are that it will take Iran 5-10 years to develop a usable nuclear bomb. So it will not be George W Bush who has to handle the situation, it will probably be his successor, and maybe the president after that. What if that president is Hillary Clinton? What if it is John McCain.
McCain is a clear defence hawk. He would demand from the joint chiefs viable options. This far in advance, it is difficult to know for certain which option would look best. But Hillary Clinton - at least if her husband's presidency is anything to go by - is easier to call.
Bill Clinton did not ignore problems abroad, but he had a visceral objection to deploying American troops. He tried to solve every problem from the air. Bombs and missiles were his only resort.
If a future President Hillary Clinton were to take the same attitude, the list of viable options to confront a near nuclear Iran would be very limited. Without even special forces on the ground to identify targets only the most devastating missile attack could possibly eliminate a substantial nuclear programme spread over dozens of sites. An attack on this scale would need to involve American nuclear power to be sure of success.
She would face a choice between a nuclear attack and no action at all. She would be sure to take the first option.