You can't really win against an enemy who's only prerequisite for continuing the effort is the will to do so, while your efforts are being undermined on the home front.
Bush and Blair both made a point to state from the beginning that they were in it for the long run, whether it was popular or not, but the circumstances are changing; the rising resistance to the deployment can't be ignored forever,even evoking the war on terror is failing to produce the desired results.
Bush may or may not be correct in assuming he can produce'victory',whatever that is, but history tells us that the pressures on and the sacrifices of the American population are likely to be a greater deciding factor than overwhelming military superiority.
As much as the right wing initially hated the Vietnam analogies, they just wouldn't go away, and how could they, being so deeply ingrained in the American psyche.
Point of interest : http://www.press.uchicago.edu/Misc/Chicago/567702.html