Well with his "you are either with us or against us speech" regarding gov'ts that support terrorism, I feel that Bush committed himself to a conflict with Iran. Not to mention the whole Axis of Evil comment and stance.
Bush attacked Iraq and the world questioned his motivations regarding his world on terrorism. Attacking Iran would be an example of him actually preemptively attacking a terrorist endorsing state.
It's not all together logical, but neither are his policies.