If General Qanbar and Mr. Maliki plan to continue shielding militias like the Mahdi Army, this new drive will be doomed before it begins.This is not an if, it's a certainty. Maliki is only in power because Sadr allows him to be, and the Bushies either don't notice or don't care. Any move to take on Sadr is doomed to failure, especially if it depends on one of his clients for success.
The three most plausible explanations I can think of for this doomed approach are:
1) Stupidity and incompetence. This can never be ruled out.
2) Looking busy. The administration wants to look like they're taking bold decisive action while they run out the clock so Iraq becomes President Gore's problem ("How's that for an inconvenient truth? In your face, Captain Nerdboy! Heheheh.").
3) Provocation. Create a military disaster that you can blame on Iran, so you have an excuse to bomb some democracy and gratitude into them.
A few thousand troops is a small price to pay for Dubya to finally achieve his lifelong goal of nuking the shit out of somebody. I'm sure the troops will be happy to make the ultimate sacrifice so that their president can experience a momentary erection. We could call it Operation Die-agra.