Just some random thoughts:
At no time, to my knowledge, has an American President seen his party lose control of Congress during time of war. The election of 2006 was a first.
The war in which this happened is one of the longest yet least bloody in the nation's history.
The casualty rate for the worst months in Vietnam was ten times as large as the worst month in Iraq.
If the Congress begins an immediate pullout of Iraq, our enemies there will have demonstrated to all the sundrie that it is not necessary to defeat our military; one need only survive, dish out a relatively small number of casualties, and the support of the American people for the struggle will evaporate.
Even greater dividends can be achieved if one is patient; with luck...the greatest proponents of military action within the U.S. might be voted out of power.
For, as some have said, Americans no longer possess the capacity for sustained struggle; unless it is for acrimonious and vitriolic political warfare.