The Revolutionary Guard now has more power than the Islamic Republic’s Supreme Leader.

At first glance, Iran’s Supreme Leader Ayatollah Ali Khamenei might seem a happy man. The pro-democracy movement had promised that last Thursday, the 31st anniversary of the Islamic Revolution, would be a turning point for the cause of freedom. But Mr. Khamenei’s regime contained the mounting opposition.

The Islamic Revolutionary Guard Corps (IRGC) controlled Tehran with the help of tens of thousands of club-wielding street fighters shipped in from all over the country. Opposition marchers, confined to the northern part of the city, were locked into hit-and-run battles with the regime’s professional goons. An opposition attempt at storming the Evin Prison, where more than 3,000 dissidents are being tortured, did not materialize. The would-be liberators failed to break a ring of steel the IRGC threw around the sprawling compound.

For the first time the regime had to transform Tehran into a sealed citadel with checkpoints at all points of entry. The IRGC was in total control. Code-named “Simorgh,” after a bird in Persian mythology, its operation created an atmosphere of war in the divided city. Warned that his life may be in danger, Mr. Khamenei was forced to watch the events on TV rather than take his usual personal tour.

Even the most successful Islamic dynasties—such as the Umayyids, the Abbasids and the Fatimids—came to depend on mercenaries known as the Mamluks, who were recruited from pagan tribes of Central Asia. Often the Mamluks seized power by murdering the caliph or keeping him as a puppet.

The IRGC is a modern version of the Mamluks. Their leaders are more strident than many of the regime’s leaders, vetoing countless attempts by mullahs and politicians to reach a compromise with the portion of the opposition still calling for reform rather than regime change. Revolutionary Guard generals frequently appear on television to call for mass arrests and show trials. A weak and indecisive caliph, Mr. Khamenei has so far refused to endorse the kind of “final solution” the generals demand.

Mr. Khamenei has other reasons to be unhappy. According to the Ministry of Labor more than a million jobs have “vanished” in the past 12 months thanks to President Mahmoud Ahmadinejad’s populist policies. In the same period, the nation’s currency, the rial, has lost a quarter of its value against a basket of other oil-based currencies in the region.

Even so-called realists must concede that the Khomeinist establishment, under the emerging leadership of the IRGC, is not the only actor on the Iranian scene. There is another actor: the popular movement for change. To ignore the democrats and fail to support them in clear and strong terms would be a sign of poor political judgment—even under the most cynical version of realpolitik.