If keeping Iran isolated in its own neighborhood was imperative for American interests and security, then we basically acted in direct contradiction to that specific interest.
We could also draw another lesson from the growth of Iranian influence and power following the invasion of Iraq, and this is that policies that are supposed to increase and advance American power can be short-sighted and counterproductive. Indeed, these policies can ultimately produce the opposite result. More than that, we could conclude from this experience that the people most intent on securing and perpetuating U.S. hegemony are often the worst judges of how to do this.
Right, and as I argued yesterday, were Iranian influence in Iraq not marred by the ever-nebulous and changing concept of "American interests," we'd likely be cheering and gushing over such short order rapprochement between two bitter enemies.
And it should go without saying that there indeed are negative consequences for the United States should Iran exerts too much influence in Baghdad - especially if those interests are anything close to what we were told they'd be in 2003 and onward. Indeed, if keeping Iran isolated in its own neighborhood was imperative for American interests and security, then we basically acted in direct contradiction to that specific interest (there's a reason Iran rolled out the red carpet for the invasion of Afghanistan, after all).
And I believe the problem, as Larison notes, isn't just the policy, but the policymakers. The goalposts are constantly being moved on American interests in the Middle East, as wonks and writers jump from one bogeyman to the next. But this isn't strategy, it's just reaction; a bouncy ball of central front-ery.