The Democrats, at least as far as the Presidential candidates and their strategist go, are sure that the Iraq war can be won, and that it will be obvious to most American's that it can be won by election time, 2008.
That's why they are so desperate to legislate a defeat for US forces, and a victory for al Queda.
The war was a huge asset to the Democrats in 2006. I don't think there is a single person on the planet that doesn't acknowledge that the Democratic Party takeover of the House and Senate was engineered on the back of the "anti-war" movement. I'm pretty sure that MoveOn.org and the Krazy Kos Kids will back me on that. Hell, AW would probably back that statement. The American public, fed a constant diet of half-truths and outright lies by the media and the Democrats, voted to change course. As is their right.
So why are the Democrats desperate to get rid of this cash cow and red herring? Because the war only works as a Democrat Party asset when it's not going well. If the Democratic Party candidates believed what they say, that the war is lost, it can never be won, then they would be far more willing to keep it going in order to use it as a campaign platform. Does anyone honestly believe that Hillary wouldn't be willing to sacrifice a few thousand more soldiers and a couple hundred billion of your tax dollars in order to have a failed Iraq War in 2008 to throw in the face of any Republican candidate? And to hold up to the American public as the (likely only) reason to vote for her? Of course she would. And it's not just Hillary, I can say the same of every single Democratic Party candidate. Most all of them loathe the military, and would be perfectly happy to keep is dying in large numbers if it meant that they could gain a percentage point or two on election day.
That fact cannot have completely escaped the minds of the political advisors to the Democrats. It cannot have escaped their minds that if the war is showing clear signs of success, that each and every "defeatocrat" will look like the traitor that they are, and the public will vote accordingly.
So which seems more likely. That the Democrats in Congress, desperate to get their man in the White House, are willing to end a war that (if it is going as badly as they tell their constituents it is) they know would guarantee a Democratic victory in 2008? Or that the Democrats in Congress, knowing perfectly well that the war is likely to show progress by 2008, are now willing to legislate a defeat for US forces and a victory for al Queda?
People have asked, "Why legislate a deadline?". They are not legislating a deadline, they are legislating a defeat. The deadline, months before the election, which means troops would have to start their retreat at least a year before the election, is meant to ensure that the image of the Iraq war is that of retreat and defeat. The Democrats cannot afford even the slightest indication of an Iraq War going well. In the end, the Democrats are more worried about a Republican victory in 2008 than they are an al Queda victory in 2008.