Actually, i think it’s a bit more cynical than that. The Dems don’t want to actually impact anything in Iraq. That would make them responsible for the results. Granted, the majority of Americans appear to want the war over. However, let’s say them Dems cut off funding, Bush brings the troops back home, and a massive civil war breaks out in Iraq drawing in Turkey, Syria, Iran, etc. (the likely result of removing troops now) Hundreds of thousands dead, massive ethnic cleansing, not to mention possible terrorist strikes on the U.S. If that occurs, what will the American public think of the Dems move to pull the troops out? They will likely view them as incompetent and that will impact the results of the 2008 election.
The Dems simply want to be seen as opposing an unpopular war, they don’t really want to take responsibility for the alternative.