Populist Moktada al Sadr, a thorn in the side of the American military as well as Iraqi officials since 2003, won big in Iraq's elections last week. After a snub by Americans in 2003, al Sadr led the Shiite insurgency, which the U.S. military wasn't able to quash till 2008. He made a comeback in last year's provincial elections, and is increasingly considered part of mainstream Iraqi politics. Though he's still living in Iran, al Sadr's followers waged a disciplined campaign and are set to have more power than ever in post-invasion Iraq. The Sadrists' rise could complicate the forming of an Iraqi government; they're unpredictable, and now their bloc could be as big as 40 seats and as large as the Kurds', who've been able to play kingmaker since 2005. Sadrists no longer back Nouri al Maliki, which is bad news for the prime minister, and they're quickly eclipsing Shia leaders who returned from exile after the invasion.