Imagine if, as public and Congressional discussion about the prospect of going to war against Iraq reached a peak in the autumn of 2002, it somehow could have been foreseen that nine years later there would still be debate about U.S. troops in Iraq, and about whether to keep them there even longer than nine years. The prospect of U.S. involvement in a war in the Middle East dragging out that long would have killed the possibility of neocons being able to conduct their great experiment in trying to inject democracy through the barrel of a gun—notwithstanding even the post-9/11 militant mood of the American public that, in the real world of 2001-2003, made it politically possible for the neocons to launch their experiment. The war would never have happened. Recreating our own thoughts from a decade ago, free of the political and emotional baggage accumulated during the course of this long expedition, provides necessary perspective in assessing what is being said today about keeping U.S. troops in Iraq or finally bringing them home.

With President Obama's announcement Friday about Iraq, we can look forward to an extra reason to celebrate during the year-end holidays. This long national nightmare will finally be ending. The return of the last combat troops from Iraq will be a good time to reflect on the nature and broader consequences of what future historians will regard as one of the biggest blunders in U.S. history. That reflection can consider how a small number of determined advocates of war were able to use the post-9/11 political milieu and scary themes about dictators giving weapons to terrorists to get enough people to go along with their idea. The reflection also can consider the full range of costs and damage to U.S. interests, from the more than four thousand Americans dead and tens of thousands wounded, to the trillions of dollars of direct and indirect fiscal and economic losses, to the tarring of America's standing abroad and the boost the war gave to America's extremist enemies.

For now, however, there is the immediate subject of bringing home those remaining troops. In response to any doubt that this is the right thing to do, the main question to ask is: if not after almost nine years, then when? Given that the troops' return merely fulfills an agreement that the previous U.S. administration reached with Iraq, one could also ask: if not George W. Bush, then who? Yet another question is: if the purpose of being in Iraq is supposedly to help another nation in need, why would we want to stay if the other country doesn't want us? Iraqi preferences have varied, of course, but being unwelcome is a very large part of what the misery of this war has been about, including the stimulation of armed resistance to what was seen as a foreign occupation. Discussions in recent months about possibly extending the U.S. military presence beyond this year took the odd form of the United States doing most of the asking and Iraq doing most of the resisting.

This is hardly the first war that exhibits the common tendency to think that just a little more persistence will make the difference between a win and a loss. But this tendency is no more logical than a gambler on a losing streak doubling down on his bets. There is no reason to believe that the next year or two of war will be more productive than the previous year or two or three. As with other lights that have been seen at the end of other tunnels, this kind of incremental thinking is a prescription for winding up with far greater costs than would justify even something that could be described as a win. We are dealing in the realm not of logic but of psychology, especially with the common but mistaken human inclination to treat sunk costs as investments.

The president's announcement will set off a new round of recriminations and debating points. Opponents of the president and proponents of the war will stake out positions to enable them to say, in response to anything nasty that happens henceforth in Iraq, that the problem was we withdrew too soon. Republican presidential candidates are of course among the first out of the blocks in doing this. Mitt Romney fired off a strongly worded statement that referred to the president's “astonishing failure to secure an orderly transition in Iraq.” (What transition are you referring to, governor? From Maliki to someone else? How long will that take? And what could U.S. troops do about it?) Michele Bachmann said, “In every case where the United States has liberated a people from dictatorial rule, we have kept troops in that country to ensure a peaceful transition and to protect fragile growing democracies.” (Kept them there how long? And which countries are you referring to, Ms. Bachmann? Will we be stationing troops in Libya?)

Then there are the intellectuals who have had the biggest professional and psychological investments in the Iraq War. Only some of them have acknowledged the war was a mistake. There is a lot of cognitive dissonance to relieve. We already saw the relief process begin several years ago, when the war first went unambiguously sour and the scapegoating began. Some of those outside government who had been the most fervent proponents of the war also became the harshest critics of how the war was conducted, with the Bush administration as a whole and Donald Rumsfeld in particular being scapegoats. The message was that the war wasn't a bad idea; it was just executed poorly. Now there will be the added message that the war was still supposedly a good idea, but it just wasn't waged long enough. Frederick Kagan has fired an early shot along this line under the heading of “Obama abandons Iraq.” The most noteworthy thing about Kagan's shot is that it is centered around the notion that withdrawing U.S. troops will undermine containment of Iran—noteworthy because the Iraq War itself has provided the single biggest boost to Iranian influence in the Persian Gulf region.

President Obama inherited multiple messes, at home and abroad, from his predecessor. Some of those messes, especially the lingering effects of the Great Recession, are proving hard to clean up. But congratulations, Mr. President, for bringing to a conclusion the biggest overseas mess you were given.