Despite the huge protests on the streets of Tehran, Iranian President Mahmoud Ahmadinejad has once again triumphed. A relative newcomer to Iran's political scene, Ahmadinejad's re-election and subsequent crackdown on the demonstrators suggest that the Iranian political system is moving in a new and potentially dangerous direction.

The re-election appears to have depended on systematic fraud, as alleged by vocal opponents. What it represents is a defeat for Iran's ruling clerical class, led by such revolutionary luminaries Ali Akbar Hashemi Rafsanjani - and a victory for the increasingly powerful Islamic Revolutionary Guards Corps, who are in many ways the real power behind the upstart Ahmadinejad.

The Guards indicated even before the election that they would not allow Ahmadinejad's challenger, Mir Hussein Mousavi, to succeed. And they are willing to use any means possible, including mass arrests of opposition leaders and the use of military force against protesters, to maintain their grip on power. Iran's ruling political elite have earned much popular hostility in the last few days, but they appear to have enough military support to withstand the protests for now. Regardless, the Islamic Republic may no longer be able to count on the people's will to maintain its legitimacy

The result has serious implications for the Iranian people - including continued social repression, economic mismanagement, and the stifling of political dissent - and for the international community, especially the United States. The Guards' continued political ascent and their military aspirations, including expanding missile and nuclear programs, will pose a new challenge to the Obama administration's efforts to engage Iran.

In a pre-election televised debate with Mousavi, Ahmadinejad attacked some of the Islamic Republic's leading luminaries, including Rafsanjani, for being corrupt and out of touch with the people's needs. But Ahmadinejad's attack on Rafsanjani was also an attack on the political status quo and the clerical class that has ruled Iran for the last 30 years.

Significant segments of the Iranian population, including the rural population and the lower religious classes, have embraced the seemingly humble Ahmadinejad as one of their own. More importantly, high-ranking members of the Revolutionary Guards and the paramilitary Basij have formed a powerful network that has provided Ahmadinejad crucial support during the last two presidential elections. The Ministry of Interior and Iran's broadcast agency, which announced the election results before all the votes were tallied, ,are both run by former Guards commanders and Ahmadinejad allies.

With this election, Iran appears to have entered a post-revolutionary era, one that will no longer be dominated by clerics such as Rafsanjani or by former President Mohammad Khatami, whose efforts at reform were largely unsuccessful and even aided the Guards' rise. Both men, along with Mousavi, were the leading proponents of U.S.-Iranian dialogue and more "democratic" governance. Their exclusion from the political system, in addition to Supreme Leader Ali Khamenei's endorsement of Ahmadinejad, may lead to an increasingly repressive Iranian state willing to use force to maintain its grip on power.

The United States will also face an increasingly militarized Iran with grand regional ambitions. The Revolutionary Guards are not only the dominant economic and political players at home, but also drive Iran's national security strategy, especially in Iraq, Afghanistan, and the Persian Gulf. They also manage its growing missile inventory and will command Iran's nuclear weaponry, if the leadership opts to create them. In short, they hold the keys to Iran's future, and their hand has now been strengthened.

Not that all hope for diplomatic progress is lost. Khamenei and Ahmadinejad have indicated some interest in limited engagement and cooperation with the United States, given the right conditions. But the Guards, buoyed by what they claim was a "landslide" election victory and continued U.S. preoccupation with Iraq, Afghanistan, and Pakistan, are now more likely to conclude that Iran has the ultimate advantage in any negotiations with the Obama administration.

"The United States must recognize Iran as a powerful state," General Yahya Safavi, a former Guards chief commander, has told journalists. The Guards, once they have crushed their opponents at home, will not be in the mood for compromise with the United States, their chief remaining adversary.

Alireza Nader is an international security associate at the RAND Corporation, a nonprofit institution that helps improve policy and decision-making through research and analysis.