Iraq's government draws support from the country's majority Shiite community, possesses the considerable advantages of being an internationally recognized sovereign state, has access to vast oil revenue, and is able to avail itself of weapons and training provided by the United States of America during a years-long period of tutelage.

So why is it unable to field a military force capable of standing up to the numerically smaller, poorer, worse-equipped, and less-trained fighters of the Islamic State of Iraq and the Levant (ISIS)? Congressional Republicans know the answer: Barack Obama.

"Everybody in his national security team, including the chairman of the Joint Chiefs of Staff, ought to be replaced," said John McCain.

"It appears to me that the chickens are coming home to roost for our policy of not leaving anybody there to be a stabilizing force," according to Senator Roy Blunt.

Many pundits agree. Reihan Salam argues that keeping American military forces in Iraq would have simultaneously strengthened the central government while also restraining it from undertaking policies that alienated the minority Sunni Arab community. Richard Haas says that "after inheriting an improved Iraq, thanks to the surge undertaken by the George W Bush administration, [Obama] should have pushed harder for a residual US or international force to remain." This force "could have damped local rivalries and trained Iraq's army."

The logic on display here shows the toxic self-justifying nature of American military adventures. If a war accomplishes its stated objectives, that goes to show that war is great. If a war fails to accomplish its stated objectives — as the Bush-era surge miserably failed to produce a durable political settlement in Iraq — then that simply proves that more war was called for.

But there is simply no reason to believe that the presence of American soldiers in Iraq makes a durable political settlement more likely, and there never has been. If eight years weren't enough, why would one more — or two more or twenty more — be the key to success?

The truth is the opposite. The speed with which the apparent gains of the surge melted away in the face of Iraq's entrenched domestic political problems underscores how futile the US-led campaign there was.

The US military is the finest military in the world, the sharp spear of the mightiest empire in human history. But the considerable virtues of America's fighting forces do not give it any particular expertise in micro-managing Iraqi politics. And the fundamentals in Iraq have simply never been very good for a peaceful and democratic settlement. The country is not only divided between sectarian groups, but sandwiched between two rival regional powers, with Iran tending to favor Shiite interests, Saudi Arabia tending to favor Sunni ones, and neither power having any particular interest in democracy and pluralism. Throw in the well-known phenomenon of the oil curse and the country's lack of stable institutions, and you've got a recipe for problems, problems that a bunch of heavily armed young people — no matter how well-intentioned or well-led — are not capable of solving.

And of course the reality is that nobody would ever have claimed otherwise (does anyone think a US military occupation would magically produce a stable democracy in Egypt?) except for the fact that American boots were already on the ground in Iraq. But the invasion that led to their presence was a tragic mistake — one driven as we now famously know by the entirely erroneous presupposition that the American people were threatened by Iraq's nonexistent nuclear weapons program.

In the finance world, banks sometimes make bad investments and end up insolvent. Regulators then need to step in and take prompt corrective action to rescue as many of the remaining assets as possible. The reason is that, from a management point of view, once your firm is already insolvent then there's no reason to worry about additional losses. You're going bankrupt and getting fired anyway. The self-interested strategy is to start gambling recklessly with the depositors' remaining money, in desperate hope that you'll strike it lucky and end up back in the black before anyone notices.

That is essentially what we were doing in Iraq for the past ten years.

Nobody would have suggested invading the country for no reason and then mounting an open-ended military occupation in the vague hope that something good would happen. One of the great virtues of Obama's election was that with his hands personally clean of the original sin of invasion, he was able to judge forward-looking policy on the merits. The situation in Iraq was a mess, but a mess that the United States of America was not capable of fixing. That was true in 2003 and it was true when our troops left and it remains true today.

Sending in the Marines and hoping for the best is no more likely to work than keeping the Marines out and hoping for the best, and it never has been. Admitting that we made a mistake and that the wisest course was to cut our losses and get our troops out was one of the best calls Obama ever made.