Tyler Cowen explains why the real costs of war with Iraq are even higher than they seem. I'm not so sure about this, though:

The American public simply does not have the stomach for fighting a costly, potentially futile war every few years. U.S. voters have already lost patience with the pace of reconstruction in Iraq, and that frustration will linger; remember, it took the country 15 years or more to "get over" Vietnam. The projection of American power and influence in the future requires that an impatient public feel good about American muscle-flexing in the past.

I dunno. If there were some unusually large attack against US forces in Iraq tomorrow, and the administration was able to adduce evidence that some of the explosive material came from Iran, and announced limited air strikes against facilities of the officially designated IRGC's Quds Force would people really rise up indignantly?