Neil the Ethical Werewolf observes:
The silver lining behind Democratic capitulation on Iraq, to talk like a mathematician, is that it reduces the 2008 election to a problem previously solved. 2006 showed us that we can destroy the GOP in an election where public anger about the continuing Iraq War is the big issue, and in 2008 we'll be replaying that scenario with 7 more GOP Senators up for re-election than last time.
Nobody seems to want to mention it because it's impolite, but I think this is almost certainly a factor in the congressional politics of Iraq. Not only are Democrats afraid of taking certain kinds of political risks to end the war, but they see no prospect of a political upside to ending it. There was a fairly overwhelming belief in Washington in mid-to-late November 2006 that Republicans would start moving to end the war in January. It didn't happen, but then came the belief that they would start to abandon ship in September 2007, which also didn't happen. But given that Republicans aren't doing what everyone expected them to do and reducing their political exposure on Iraq by winding the war down, Democrats are disinclined to go out on a limb to do it for them.