I think Swopa has a point here:
Given enough cognitive dissonance of endless stay-the-course rhetoric against a backdrop of military stalemate and mounting casualties, the American public will eventually say, "You're right -- we don't have the will to fight it out. Bring our boys home!"
We reached that breaking point in Vietnam, and it's rapidly approaching with Iraq.
... but here's the danger: Even though the public might reluctantly endorse withdrawing to stop the pain of the moment, they won't be proud of it. And when another threat emerges (say, due to another terrorist attack), they'll just flip-flop and go looking for another Republican strong daddy to protect them.
...As long as the debate is Dubya saying, "Be strong enough to stay the course," versus Democrats saying, "No, it hurts too much -- bring the troops home!", any political victory we win is going to turn into defeat eventually.
He's right. A few years later, a pullout will be portrayed not as a response to widespread public disgust, but as a cave-in engineered by America-hating liberal Democrats and their allies in the media. No one will remember the name John Murtha (just as, even now, no one remembers that last summer Walter Jones, a deeply conservative Republican, said much the same thing Murtha just said yesterday); the withdrawal will be blamed on Michael Moore and Cindy Sheehan and whatever Democratic officeholders work best at that moment at getting a rise out of the crowds at Republican rallies. A new Reagan will emerge, determined to help America "stand tall again." The familiar cycle will repeat.
War opponents never succeeded in framing this war as a distraction from the real enemy, al-Qaeda, and never succeeded at framing the low-troop-strength Bush/Rumsfeld war plan as unconscionable because it couldn't possibly secure peace in Iraq. Choosing to abandon the pursuit of bin Laden to fight this war made America (and the world) less safe; fighting the war Rumsfeld's way made America (and the world) less safe. This war is a failure on its supporters' own terms.
Americans want leaders who'll keep them safe. To this day no one's really made the case that George W. Bush is incapable of doing that.