Gates confirms what Bush eluded to in his speech last night and what Maliki told reporters that al-Sadr will not be protected:

Asked if the new U.S. and Iraqi offensive would go after Muqtada al- Sadr, the anti-U.S. radical Shiite cleric, Gates said, “All lawbreakers are susceptible to being detained or taken care of in this campaign.”

Sadr is a key ally of Iraqi Prime Minister Nouri al-Maliki.

(via)
Now we have to wait and see if it will actually happens.
Updated to add: Here’s another article on Maliki:

Iraq’s prime minister has told Mahdi Army militiamen they must surrender their arms or face an all-out assault by U.S.-backed Iraqi forces, senior Iraqi officials said Wednesday, revealing a pledge Washington wanted to hear as American and Iraqi troops prepared a fresh operation to end the bloody sectarian war gripping Baghdad.

The blunt message was particularly significant given that Nouri al-Maliki, the Iraqi leader, previously had blocked several U.S. attempts to crack down on the military wing of radical anti-American Shiite cleric Muqtada al-Sadr, now one of the most powerful players in Iraq.

“Prime Minister al-Maliki has told everyone that there will be no escape from attack. The government has told the Sadrists (the political movement that supports the Mahdi Army), if we want to build a state we have no other choice but to attack armed groups,” a senior Shiite legislator and close al-Maliki adviser said.