Christian Brose writes:
...one of the many tragedies of the Iraq war was that, at the moment (in April 2003) when U.S. leverage over Iran was highest, the Bush administration did not attempt to use it to change Iran’s behavior.
Chris Dierkes piles on:
In the beginning of the Afghanistan Conflict and prior to the Iraq War (2002 basically) the Iranians offered help to the US in the building of a post-Taliban Afghan government.
Since the Taliban were/are sworn enemies of the Tehran regime (bonus: oops there went the whole worldwide united Islamist threat canardkinda hard to be a united world front when you are busying fighting and killing each other). The Iranians even offered a deal whereby they would help train Afghan police under US auspices (i.e. with US training manuals, in US style, etc.).
For Iran’s (otherwise quite helpful) effort, especially via their strong connections to the Northern Alliance and being arguably the central cementing power that brought into being the Bonn Agreement, they were put in the Axis of Evil.