Baghdad ? The widening clashes between Iraqi forces and Shiite militiamen mean more than a showdown on the streets: it could be a defining moment for U.S.-backed Prime Minister Nouri al-Maliki.

Al-Maliki, in office since May 2006, is almost certain to pay a heavy political price if he fails against Shiite militias in battles that began in the southern city of Basra and then flared in Baghdad and other cities.

And he knows the stakes are high. He has promised not to compromise and vowed to battle to the end against the Mahdi Army militia led by anti-American cleric Muqtada al-Sadr.

That’s a bold position considering the fight so far.

The Iraqi campaign in Basra – launched this week to uproot Mahdi Army’s influence in the important oil center – has been bogged down in the face of strong resistance, desertions and mutiny in government ranks, security officials said Thursday.

But al-Maliki appears unshaken and has turned the fight into a personal test.

He has traveled to Basra, 340 miles south of Baghdad, to take personal charge of the operation – the first major battle waged by Iraqi forces alone without strong U.S. backup. It’s a gambit with clear fallout for al-Maliki if Iraqi security forces come up short.

His political standing would be seriously bruised at a time when he is attempting to play unifier between the nation’s three fractious groups: majority Shiites, Sunni Arabs and Kurds.

Sunni leaders, who complain of being sidelined by al-Maliki’s government, could feel emboldened and press harder for al-Maliki’s ouster. Even the prime minister’s main coalition partner – the powerful Supreme Islamic Iraqi Council – has recently been dropping hints of disapproval of al-Maliki.

Much now rides on the outcome of the showdown against the Mahdi Army, the main rival of the Supreme Council in the Shiite heartland in southern Iraq.

“If the (Iraqi government forces) cannot gradually get some control over Basra, of course al-Maliki will lose prestige,” said Phebe Marr, a historian on Iraqi affairs and senior fellow at the U.S. Institute of Peace in Washington.

But she believes his main Shiite allies will not quickly abandon him regardless of how events play out against the Mahdi Army.

A senior aide said al-Sadr is seeking a political solution. In a statement relayed by Hazem al-Aaraji, al-Sadr said he wants “everyone to pursue political solutions and peaceful protests and a stop to the shedding of Iraqi blood.”

The crisis came to a head following months of U.S. and Iraqi raids that detained hundreds of Mahdi Army fighters even as the militia maintained its self-proclaimed truce – which Washington has credited for helping bring down violence since last August.

But the timing could also be an attempt to take a swipe at al-Sadr before the Pentagon scales back its forces in coming months, from 158,000 to about 140,000.

Al-Maliki’s government, meanwhile, is looking ahead to provincial elections this year that will be a key test of its standing against al-Sadr.

“It may be a calculation that it is better to undertake this action while there are still robust (U.S. forces) in the country,” said Marr.

There is no doubt, however, that al-Maliki is acting with uncharacteristic daring.

His hallmark – and perhaps means of political survival – has been caution. Al-Maliki has been careful not to anger his Shiite political base by pushing too hard for U.S.-backed reforms, including bringing more Sunni Arabs into the security forces.

At times, Washington’s patience with al-Maliki appears to be wearing thin. But the tone changed after Iraqi forces pushed into Basra.