Henry Kissinger: You never once defeated us in battle.
General Giap: That is true. It is also irrelevant.

Victory is not defined by tactical success, but by a strategic outcome.
The explicit political goal of the Vietnam war, the preservation of the regime in the South, was not achieved. But defeat in Vietnam never led to a Communist Asia, so in that sense we did succeed in our implicit, goal. In fact; it is clear now we would have achieved that even if we never had fought in the first place.

We certainly have the power to stay in Iraq and kill Arabs indefinitely, the question is whether that will ever lead us to any meaningful strategic gains. The stated political goals of this war (as well as the implicit geopolitical ones I have often alluded to) have changed over the years to reflect the changing situation on the ground. We change our goals to justify the war, instead of waging war to achieve a goal. Perhaps the present policy may still yield dividends, I can't predict the future; but even if it does so, it will be just because we get lucky. Right now, even if we completely defeat the insurgency and restore order and rebuild a democratic Iraq economically, we still have no guarantee it will support us.