Baghdad ? A Muslim cleric who once used a militia to resist the American invasion positioned himself as a big winner in Iraq’s monthslong political deadlock Friday when his party threw its support behind the beleaguered prime minister.

The hard-line Shiite group led by Muqtada al-Sadr called it the start of its ascent to nationwide power — a specter sure to spook the United States.

Washington considers the cleric a threat to Iraq’s shaky security and has long refused to consider his movement a legitimate political entity. But Prime Minister Nouri al-Maliki may be unable to govern without him.