Does Iran's deep religious influence in Iraq translate to politics?

During the rule of Saddam Hussein, few Iranians dared to make the religious pilgrimage to the holy city of Karbala in Iraq. But the toppling of Saddam has drawn millions of worshippers back, revealing Iran's powerful influence there. In the first of three reports, special correspondent Reza Sayah explores the scope of and limits on that influence, in collaboration with the Pulitzer Center on Crisis Reporting.