Paul Pillar explains why delusional claims that the Iraq war was “won” at any point are so damaging:

The damage that the myth about Iraq inflicts is not limited to fostering public misunderstanding about an important episode in modern American history, although that is indeed harmful. It is not limited to fostering misunderstanding about who was right and who was wrong about that episode and thus who should and should not be listened to on similar matters, a misunderstanding that also is harmful. The damage extends to the encouragement of more general misconceptions about efficacy of the exertion of U.S. power overseas.

Pillar is right about all of these, but I’d like to add a few comments. Believing in the “surge” myth in particular prevents many Americans from reaching sober and informed conclusions about the wisdom of persisting in failed wars. When one accepts the falsehood that the “surge” kept the Iraq war from being lost, it becomes much easier to argue for escalating any conflict, no matter how futile it is. Saying “the surge worked!” has served as an all-purpose retort to every argument for cutting our losses, admitting failure, and minimizing the costs of a disastrous policy. It doesn’t matter that it isn’t true. It is flattering, which is so often much more appealing than the truth. It encourages the illusion that hard power can never really fail despite its obvious failures. That then encourages a stubborn insistence on continuing wars for many years after it has become obvious that a U.S. military presence in the country is having undesirable and truly harmful effects. Meanwhile, the related myth that the Iraq war was lost only after the “surge” had “won” it counsels that the U.S. should never withdraw its forces from a country once it has fought a war there, and its advocates try to get the rest of us to believe that as long as U.S. forces are still present in the country the war can never really be lost.

This myth does damage to our foreign policy debate in another way: its adherents are committed to rejecting any reassessment of the wisdom or justification of the war. That in turn makes them actively hostile to anyone that is interested in acknowledging and learning from the massive errors in judgment and understanding that made the war possible in the first place. The myth feeds the hawks’ ideological fantasy that the Iraq war was not wrong in principle from the very beginning, but only temporarily went awry because of poor execution that was corrected later. That allows hawks to advocate for hard-line and aggressive measures without having to account for the disaster of the Iraq war, because they have already convinced themselves that they and their allies had nothing to do with the failed war.