The United States missed a huge opportunity after 9/11 to influence the course of Iranian politics but, as usual, blew it. Iran, which had reason to dislike the Taliban, saw 9/11 as a opportunity to create stronger ties with the United States. They actively helped the U.S. in Afghanistan and supplied information about Al Qaeda, often actually capturing terrorists who sought refuge in Iran. Very secret negotiations were being conducted between Iran and the United States that provided support for reformer in Iran who wished to bring a more democratic regime to power.
That all changed with Bush's "Axis-of-Evil" speech that linked Iran to North Korea and Iraq, a long-time enemy of Iran, and the threat to Iran implicit in Bush's speech that we would engage in regime change in those countries. Condi Rice, who should have known better, did not recognize the import of the language and thought Bush's speech was simply a recognition of our support for democracy (despite the fact that we don't have one - one of life's little ironies.)
Reference: Bitter Friends, Bosom Enemies: Iran, the U.S., and the Twisted Path to Confrontation by Barbara Slavin