Muqtada al-Sadr - A Man for All Seasons
An interesting article on truthout.org; "In the spring and summer of 2004, the radical young Shiite cleric Muqtada al-Sadr led an armed uprising against the U.S. occupiers. His militia, the Mahdi army, fought several bloody battles against American forces...High-ranking U.S. officials called for Muqtada to be captured or killed. But the fiery cleric not only survived, but flourished - and in the last two years he has turned his enormous street credibility into political power. In the December elections his slate earned potentially 30 seats in Parliament, making him an equal partner with two other Shiite groups in the largest Shiite coalition, the United Iraqi Alliance. But what sets Muqtada apart from the other Shiite leaders - and makes him a potentially crucial, if supremely unlikely, ally for the United States - is his close ties to the Sunni insurgents. With sectarian tensions in Iraq and the region increasing, Muqtada may be the only Shiite leader in Iraq who can reach out to Sunnis, who see him as 'the good Shia.'"

Now check this bit or the article; "In recent weeks, Muqtada burnished his credentials with both the Sunni and Shiite establishments when he visited first Saudi Arabia, then Iran - where he warned the United States that if it attacked Iran, he would send his forces into the field."

So if the US attacks Iran - he will attack them along with the Sunni insurgents, who I guess will use the opportunity of this second front.