President Obama missed the boat on tax reform. He put politics above entitlement reform. He worsened already-tense relations with Israel. But the worst error, in large part because it was both avoidable and is not irreversible, was to pull all troops out of Iraq.

Peter Wehner writes:

We’re seeing a dramatic resurgence of sectarian and ethnic divisions. And the Iraqi Prime Minister, Nouri al-Maliki, issued a warrant for the arrest of Vice President Tariq al-Hashemi, a Sunni leader who has since fled to the autonomous northern Kurdish region. (Maliki has ordered the Kurds to “hand over” Hashemi or face “problems.”) This is precisely why U.S. commanders recommended we maintain a residual American force of 15,000 to 18,000, in order to keep violence down, ethnic divisions in check, and Maliki in line. But President Obama thought he knew better, and now we have no U.S. presence in Iraq to speak of. . . .

What is happening in Iraq is sickening, in part because the gains came at such a high cost and in part because what is happening there was so avoidable. Obama was handed a war that was largely won. What America had given to Iraq is what the Arab scholar Fouad Ajami called “the foreigner’s gift.” But Iraq being Iraq, maintaining an American troop presence there, separate from engaging in combat operations, was necessary if Iraq was ever to become whole again. President Obama has undone much of what had been achieved there, almost in the blink of an eye. And when the history of his administration is written, it increasingly looks as if he will be fairly judged to have been the man who lost Iraq.

It is inconceivable that President Obama would reintroduce troops or that other countries would step up to the plate in the wake of the U.S. departure. And whatever advice or counsel we now dispense has very chance of being heeded. We have no leverage.

You wonder what Gen. David Petraeus, the prime architect and implementer of the surge, must be thinking. His greatest achievement has been leveled, troops whom he commanded have died, and America’s reputation has been damaged for the president’s personal political game, or perhaps because he is a foolish man or a spiteful one, who could never accept that President George W. Bush was right and he was wrong about the surge. Petraeus was shuffled off to the CIA — in large part, many of his admirers suspect, to keep him mum and prevent him from challenging the president politically. But isn’t he now well past the time when the fiction can be maintained that the country is better off with him there than as a free agent and a critic of the president?

Perhaps he might consider resigning. And then whoever is selected as the GOP nominee will have access to the very best advice on counterinsurgency. And Petraeus will be free to speak his mind and make sure history gets the facts right.