For the purposes of this posting I shall be totally partisan, considering only what would be the best thing to insure a Democratic sweep in 2008. Also for the purposes of this posting I shall be totally cynical and not give a rat's ass for all the good, decent American servicemembers who will be killed and horribly maimed during the next several months in that wasted effort know as the Iraq War.
The best case scenario, from this point of view, is for the Democrats to continue to try every avenue available to bring the boys home as soon as possible while the Republicans stubbornly block those efforts at every turn. Congress votes to withdraw the troops; Bush vetoes; Republicans stand alone to sustain the veto. A few more months of this and Republican candidates will have a hard time convincing their own mothers to vote for them. For a heartless cynic, things are going just peachy.
The best that can happen from an idealistic POV is for American forces to withdraw while offering the competing interests in Iraq the option of international help negotiating a peaceful compromise between them. Let them look into the abyss and choose between civil war and peace. As long as the American military occupies the country both peace and compromise are impossible because neither side trusts the American presence. While we may be able to keep them from seeing the abyss we are also preventing them from seeing any advantage to peace.