TEHRAN, Iran — Less than two months ago, it was widely assumed here and in the West that Mahmoud Ahmadinejad, Iran's hard-line president, would coast to another victory in the elections today. Many reformists who sat out the vote in 2005 seemed dejected and unlikely to raise a strong challenge.
That picture has been transformed. A vast opposition movement has arisen, flooding the streets of Iran's major cities with cheering, green-clad supporters of Mir Hossein Mousavi, the leading challenger.
Ahmadinejad, seemingly on the defensive, has hurled extraordinary accusations at some of the Islamic republic's founding figures, but the tactic has served to unify a diverse and passionate body of opponents of his populist economic policies and confrontational approach to the West.
Some Iranians believe that the unruly democratic energies unleashed over the past few weeks could affect this country's politics no matter who wins.
Ahmadinejad's radical policies and personal attacks, they say, have galvanized powerful adversaries who will use his own accusations of corruption and mismanagement against him.
Ayatollah Ali Khamenei, Iran's supreme leader, who has the final say in affairs of state and prefers to avoid open conflict, may force Ahmadinejad to steer a more moderate course if he is re-elected.
But hope has often outpaced reality in Iran, and similar democratic movements have been stifled in the past by the country's clerical leadership. In 1997, a burst of student demonstrations was followed by mass arrests, and a broader crackdown has taken place since Ahmadinejad succeeded his reformist predecessor, President Mohammed Khatami, in 2005.
Mousavi himself is no liberal. Another candidate, Mehdi Karroubi, is more closely associated with the core causes of the Iranian reformist movement, including the freeing of political prisoners and women's rights.
There are also limits to what any Iranian president can do. Although Ahmadinejad has tried to augment the powers of the presidency, it is Khamenei who influences foreign policy.
Mousavi is also critical of Iran's support for militant groups like Hezbollah and Hamas, saying the government should focus on domestic problems instead.
Perhaps more important to Iranians, Mousavi would change economic policy; Ahmadinejad has been criticized for economic stagnation, including rising inflation and unemployment. A former prime minister in the 1980s, Mousavi is credited for managing Iran's economy effectively during the war with Iraq.