Rod Dreher cites  a New York Times report  on extensive Iranian influence in Iraq. The report is correct when it says “Iran won, and the United States lost” as a result of the Iraq war. It is on much shakier ground when it asserts that “the 2011 withdrawal of United States forces…seemingly opened a door for Iran.”
Of course, TAC and other antiwar conservatives and libertarians were warning about removing a bulwark to Iranian power in the region before the invasion, and we continued pointing out the gains Iran had made in the years that followed. The process of “handing over” the country to Iran’s orbit was already happening while the U.S. was occupying Iraq with more than 150,000 troops, so it is hardly a new development and it would not have been prevented or undone by keeping 10,000 soldiers there. The prospect of Iranian power wasn’t our principal objection to the war, nor was it the most important, but opponents of the Iraq war could see very clearly before and after it happened that overthrowing Saddam Hussein would benefit Iran’s government.
Supporters of the invasion deluded themselves (or lied) when they argued that toppling the Iraqi government would undermine other authoritarian regimes in the region, including Iran’s, and they failed to anticipate  one of the most easily foreseeable results of the war they backed. Failing to anticipate likely consequences of war isn’t unusual for interventionists, but they were particularly inept in this instance. There is no question that Iran has far greater influence in Iraq after the war than it did before, but this was obvious a decade ago and was hard to miss even before that.
That is not a problem for the U.S. to “solve” now, but it is a direct result of stupid, aggressive policies that the people that now advocate for hostility towards Iran supported at the start of this century. One lesson to draw from all this is that hawks are notoriously bad at estimating the likely effects of their preferred policies, and the policies they support almost always backfire and produce worse outcomes. Hawks have had an uncanny knack for backing the policies that boost Iranian influence in the region after claiming that they will do the opposite, and that is one more reason why we should ignore their policy recommendations.