BAGHDAD -- The followers of Moktada al-Sadr, a radical cleric who led the Shiite insurgency against the American occupation, have emerged as Iraq's equivalent of Lazarus in elections last week, defying ritual predictions of their demise and now threatening to realign the nation's balance of power.

Their apparent success in the March 7 vote for Parliament -- perhaps second only to the followers of Prime Minister Nuri Kamal al-Maliki as the largest Shiite bloc -- underscores a striking trend in Iraqi politics: a collapse in support for many former exiles who collaborated with the United States after the 2003 invasion.

Although rivals disparaged the Sadrists' election campaign, documents and interviews show an unprecedented discipline that has thrust the group to the brink of perhaps its greatest political influence in Iraq.

The outcome completes a striking arc of a populist movement that inherited the mantle of a slain ayatollah, then forged a martial culture in its fight with the American military in 2004.

After years of defeats, fragmentation and doubt even by its own clerics about its prospects in this election, the movement has embraced the political process, while remaining steadfast in opposition to any ties with the United States. It was never going to be easy to form a new postelection government -- and the Sadrists' unpredictability, along with a new confidence, may now make it that much harder.