The level of investment being made in Iraq is not indicative of short term planning, they are there for the long haul. Politically they can not justify taking the overwhelming oppressive force tactics they would prefer.
It would require -
More death and destruction if they want to totally vanquish - that would not look good to the world or most of the American people
More soldiers over there which would mean the draft - that has to wait for next year
A ramped up Defense budget for the extra equipment they need and to replace what they have lost - gotta wait till next year here too
Being more obvious about their intentions - it is better to keep the American people in the dark on complicated matters they don't fully understand. We don't have time to explain!
They are content with the overall strategy that allows them broad control of the country. Eventually the new Iraqi leaders, their police/militia, combined with the "transparent" mercenary groups will take care of the local insurrections. They can then pretend their hands are not dirty - "Those other guys did that, we refer all questions on that event to their spokespeople".
Sure, they are going through a rough political/military patch now. Based on Sistani's reaction so far, it looks like he is complicit or at least acquiescing. They are quite possibly doing this as "housecleaning" before the turnover. Their mentality is similar to those who say, "If you want to make an omelet, you have to break some eggs".
From an article on the bases being built in Iraq -
U.S. engineers are focusing on constructing 14 "enduring bases," long-term encampments for the thousands of American troops expected to serve in Iraq for at least two years. The bases also would be key outposts for Bush administration policy advisers.
The number of U.S. military personnel in Iraq, between 105,000 and 110,000, is expected to remain unchanged through 2006, according to military planners.
"Is this a swap for the Saudi bases?" asked Army Brig. Gen. Robert Pollman, chief engineer for base construction in Iraq. "I don't know. ... When we talk about enduring bases here, we're talking about the present operation, not in terms of America's global strategic base. But this makes sense. It makes a lot of logical sense."
Brig. Gen. Mark Kimmitt, deputy chief of operations for the coalition in Iraq, said the military engineers are trying to prepare for any eventuality.
"This is a blueprint for how we could operate in the Middle East," Kimmitt said. "[But] the engineering vision is well ahead of the policy vision. What the engineers are saying now is: Let's not be behind the policy decision. Let's make this place ready so we can address policy options."
Not typical behavior for organizations that can conceive of "bugging out". Spending "invisible" billions just in case the policy might require it?