How much has changed for Iran in one occasionally breathtaking month. The erratic uprising is becoming as important as the Islamic revolution 30 years ago — and not only for Iran. Both redefined political action throughout the Middle East.

The costs are steadily mounting for the regime. Just one day before the June 12 presidential election, the Islamic republic had never been so powerful. Tehran had not only survived three decades of diplomatic isolation and economic sanctions but had emerged a regional superpower, rivaled only by Israel. Its influence shaped conflicts and politics from Afghanistan to Lebanon.

But the day after the election, the Islamic republic had never appeared so vulnerable. The virtual militarization of the state has failed to contain the uprising; its tactics have further alienated and polarized society.

At its summit in Italy last week, the Group of Eight industrialized nations "deplored" the post-election crackdown and urged "democratic dialogue" with the opposition. At his news conference there, Obama noted the G-8's "strong condemnation about the appalling treatment of peaceful protesters post-election in Iran" and "behavior that just violates basic international norms."

Given its advancing nuclear technology and regional influence, Iran believed before the election that it held the trump cards in any negotiations. Now, politically disgraced, it is the needy one. Washington might also pay a price for engaging with a government that brutalizes its people. Any involvement could effectively bestow legitimacy on a disputed election.

The uprising has transformed Iran's political landscape. Over the past month, dozens of disparate political factions have coalesced into two rival camps: the New Right and the New Left.

The core of the New Right is a second generation of revolutionaries, called principlists, who have wrested control of the security instruments and increasingly pushed their elders aside — at least for now. It includes Mojtaba Khamenei, the supreme leader's son and chief of staff; Mojtaba Samareh Hashemi, a presidential adviser and campaign manager; Intelligence Minister Gholam Hossein Mohseni-Ejehei; and Interior Minister Sadegh Mahsouli.

The New Left is a de facto coalition of disparate interest groups that found common cause in anger after the election. Its organization, tools and strategy are weak, but it is the most extensive coalition since the 1979 revolution. The New Left includes former presidents, cabinet ministers and members of parliament as well as vast numbers of young people and the most politically active women in the Islamic world.

What was a political divide has become a schism. Many Iranian leaders served time together in the shah's jails; today, their visions of the Islamic republic differ so sharply that reconciliation would be almost impossible.

What happens next will be determined by three factors: leadership, unity and momentum.

The opposition is most vulnerable on leadership. The big unanswered question is whether Mousavi, a distinctly uncharismatic politician, can lead the new opposition over the long term. Without dynamic direction, the opposition may look elsewhere.

Momentum may be the decisive factor. The regime will need to shift public attention to President Mahmoud Ahmadinejad's second-term agenda. For the opposition, the calendar of Shiite rites, Persian commemorations and revolutionary markers is rich with occasions to spark demonstrations. The opposition also has supporters in Iran's parliament who are likely to challenge Ahmadinejad's cabinet choices and economic proposals.

Further arrests and future trials could also spark new tension. With each flash point, the regime's image is further tainted, its legitimacy undermined.

Robin Wright, a former Post reporter, is a public policy scholar at the Woodrow Wilson International Center for Scholars. She wrote this commentary for The Washington Post.