In the past ten days, the US-led Coalition effort to rebuild Iraq as a stable, unified, and democratic state has fallen into crisis. The most alarming aspect is not the Baathist-inspired violence in Fallujah, bloody and horrific though that fighting has been. This has been a limited uprising from the minority Sunni section of the country, many of whose politicians have now entered the peaceful political game. It does not threaten the overall viability of the political transition program in Iraq.

The Shiite uprising that began a few days ago is another story, however. Scholars and historians of Iraq have long warned that an uprising among the Shia would spell doom for the Coalition, and for any hope of peaceful transition to a decent form of governance. We are not yet facing a generalized Shiite resistance. Rather, we are locked in a confrontation with a ruthless young thug, Muqtada al-Sadr, who leads an Iranian-backed, fascist political movement that spouts a shallow mix of Islamist and nationalist slogans in a bid to conquer power.

Among most Shia -- including, crucially, Iraq's most widely revered religious leader, Ayatollah Ali al-Sistani-Muqtada Sadr is a reviled figure, a crude street tough with no religious qualifications and no positive political program, who has used coercion and intimidation as a substitute for genuine religious knowledge and authority. Unfortunately, however, since the Coalition began a crackdown ten days ago on his malicious operation, Sadr has maneuvered brilliantly to portray himself as the leader of a broader nationalist and Islamist insurgency. Now, growing numbers of frustrated and marginal young Iraqi men -- including it appears, some Sunni elements -- are rallying to his cause.

If we do not confront this new resistance in a politically agile and militarily forceful and adept manner, everything we have done to help Iraqis rebuild their country as a democracy could unravel in a matter of weeks.

The democratic transition is moving forward, in many inspiring ways. With US assistance, civil society is organizing, political parties are beginning to mobilize, and hundreds of "democracy dialogues" are discussing the country's constitutional structure and future. Two UN teams are consulting with Iraqis on how to structure the interim government that will assume power on June 30, and how to structure and administer the elections for a transitional government, due by this December or January.

However, elections can only go forward and the transition succeed if the agents and means of violence are brought under control.

Underlying the current upsurge in violence has been the mounting problem posed by heavily armed militias in the Shiite south. Loyal to political parties and religious militants, riven by factional divides, determined to impose an Iranian-style theocratic dictatorship, and lavishly armed, funded, and encouraged by various power factions in Iran, these radical Islamist militias (as well as Sunni and Kurdish peshmerga militias in the north) have been casting a long shadow over the political process in Iraq. In many provinces, the militia fighters outnumber and certainly outgun the new Iraqi armed forces.

Several Islamic fundamentalist parties have been playing a clever double game. As their representatives in Baghdad negotiate and compromise with other parties, exhibiting sweet reason and moderation, their militias have been stocking heavy arms, menacing opponents, and preparing for the coming war in Iraq.

Unless the militias are demobilized and disarmed, a transition to democracy in Iraq will become impossible. Rather, at every step of the way -- from the formation of parties, to the registration of voters, to the election campaign, to the casting and counting of votes -- the democratic process will be desecrated by violence, fear, and fraud.

Key officials within the Coalition Provisional Authority (CPA) have begun to recognize the urgency of this issue. Over the last three months, a plan has quietly been prepared and negotiated for the comprehensive disarmament, demobilization, and reintegration of all the major militias. But this plan, which relies heavily on financial and employment incentives for voluntary compliance by the major militias, can only work if all the militias are disarmed. Those forces that will not negotiate and cooperate must be confronted and disarmed by force.

This brings us to the events of the last week, to the person of Muqtada Sadr, and to the biggest, most ruthless militia that stands indefatigably outside any process of negotiation and voluntary disarmament. A fiery thirty-one-year-old mullah, whose father and brothers were martyred in the Shiite resistance to Saddam, Muqtada has nothing of the Islamic learning and sophistication that would put him anywhere close to the religious stature and authority of an Ayatollah. But he knows how to organize, mobilize, and intimidatehas used the reputation of his father among the poor urban masses, and the language of historic resistance to external impositions, to mobilize a growing following among downtrodden young urban men in particular. His support is confined to a small minority among the Shia of Iraq, but it is the kind of minority, demographically, that makes revolutions and seizes power, and its devotion to his declarations and obedience to his commands is apparently intense.

In recent months, Sadr's militia -- the al-Mahdi Army -- and his loose political movement that surrounds it have been growing alarmingly in size, muscle, and daring. They have seized public buildings, beaten up university professors and deans, taken over classrooms and departments, forced women to wear the hijab, set up illegal sharia courts, imposed their own brutal penalties, and generally made themselves a law onto themselves. As with the Nazis or any other totalitarian movement, all of this street action and thuggery is meant to intimidate and cow opponents, to create the sense of an unstoppable force, and to strike absolute fear into the hearts of people who would be so na?ve as to think they could shape public policy and power relations by peaceful, democratic means.

As with the Nazis, Muqtada has been guilty of brazen crimes well before his effort to seize power openly. A year ago, Sadr's organization stabbed to death a leading moderate Shiite cleric, Ayatollah Abdel-Majdid al-Khoei, who would have been a force for peaceful democratic change and a dangerous rival to Sadr. The murder took place in the Imam Ali mosque, Shiite Islam's holiest shrine. That is the level of respect that Sadr manifests for his own religion. Just three weeks ago, on the night of March 12, apparently in alliance with fighters from other Shiite militias and with the local Diwaniyya police force, the Mahdi Army invaded the Gypsy town of Qawliyya after a dispute over what Sadr's forces alleged were morals violations by the town. After pumping round upon round of automatic rifle fire, mortars, and RPGs into Qawliyya, the Mahdi Army brought in bulldozers and literally leveled a town of some thousand people. We still do not know how many people died in this blatant act of ethnic cleansing (as the towns folk had been warned in advance of the impending doom, and many if not most were able to flee). But at the very least, Iraq now has hundreds of internally displaced people from this incident of terror, and eighteen refugees apprehended by Sadr's forces endured ten days of brutal beatings in the organization's detention center. By the logic of Muqtada Sadr, this is the kind of "rule of law" Iraq needs.

In recent weeks, Sadr's propaganda, both in his oral statements and through his weekly newspaper, the Hawza, have become increasingly incendiary, propagating the most outrageous and explosive lies (for example, that the US was responsible for recent deadly bombings) deliberately designed to provoke popular violence. Finally, on March 28, after months of costly delay, the Coalition finally began to move against this monster. Ambassador L. Paul Bremer ordered the closure of the newspaper, and Muqtada Sadr reacted by ordering his followers to rise up violently against the Coalition. Perhaps in response, the Coalition finally ordered the arrest on April 4 of a senior Sadr aide, Mustafa al-Yacoubi, and 24 others -- including Sadr himself -- for the murder of al-Khoei. About half the suspects, including Sadr, are still at large.

Sadr responded to these arrests by unleashing a revolutionary campaign to seize power. Having already stormed numerous public building in recent months, his followers took over the offices of the Governor of Basra and assaulted police stations in several cities, including Karbala with its sacred Shiite religious shrines to the Imam Abbas and the Imam Husayn. In Najaf his followers invaded Shia Islam's holiest center, the Shrine of the Imam Ali. These attempted power grabs are not new. Last October, Coalition forces intercepted 30 busloads of a thousand heavily armed Sadr followers as they were headed down from Baghdad to Karbala to seize control of its shrines and the central city.

On Monday, the Administrator of the Coalition Provisional Authority in Baghdad, L. Paul Bremer III, declared Muqtada Sadr an "outlaw." Now there is no turning back. If any kind of decent, democratic, and peaceful political order is to be possible in Iraq, the Coalition will need to arrest Muqtada Sadr, crush his attempt to seize power by force, and dismantle his Mahdi army.

We are now embarked on a dangerous and bloody campaign in which, tragically, many more American, other Coalition, and Iraqi lives will be lost. But if we do not confront this military challenge now, while we work to rebuild a broader consensus among Iraqi political forces on the rules of the game and the shape of the new political system, we will lose the second war for Iraq, with frightening implications not only for the peace and stability of that country and the wider region, but for our own national security.