The trouble is that the war's rationale has become circular -- "success" means success at putting the military engagement on a sustainable basis. We're fighting for the ability to keep on fighting. But sustaining that posture keeps making the United States and our position in the world as a whole weaker and weaker.
Success has been defined down so that now the “surge” has succeeded in stabilizing the conflict so that the United States can reduce the number of troops in Iraq to pre-surge levels. Mind you, the success we're hearing about is not an end to the conflict but stabilization of it (for now). We’re fighting for the ability to keep on fighting while steadily losing ground to enemies and losing credibility with allies both in and out of Iraq. That’s some success.
Macgregor’s article can be found here.