The murder in Panjwai of sixteen civilians, including nine children, by an American soldier on March 11 puts an exclamation point on ten and a half years of failed war in Afghanistan.

Following repeated US bombings of wedding parties, countless dead civilians as a result of night raids and drone strikes, atrocities by the notorious “kill team” in 2010 and, in 2012, the digitally recorded image of US troops urinating on dead Afghans and the burning of Korans, the United States is far from success in its longest-running imperial misadventure.

The American occupation of Afghanistan has, at least by most conventional measurements, lasted longer than our disaster in Vietnam. The original rationale for military operations—the decimation of Al Qaeda to the point of irrelevance—was accomplished long ago, yet nearly 90,000 American soldiers are still tramping across Afghan farms and hillsides and dusty streets in a vain attempt at nation-building. We have spent hundreds of billions of dollars in that effort, with painfully evident results: the government of Afghanistan is virtually nonexistent outside its shaky grip on Kabul.

A decade ago, few Afghans mourned the overthrow of the oppressive Taliban regime. Yet now, after a US occupation that has empowered warlords, fueled ethnic and tribal differences, and enriched a corrupt officialdom, the Taliban have rebounded, especially in the Pashtun south and east, where they have easy resupply from safe havens across the border under the protection of Pakistan’s army and intelligence services.

In the past six months things have taken a poisonous turn, as the long-building mutual resentment between the Afghan people and the US military has broken out in the open. This has provided an unexpected gift to Taliban recruiters and further undermined President Obama’s Afghan policy. His troop surge was designed to stabilize the country and set back the Taliban in advance of peace talks. They may now decide to forgo talks and await the inevitable US withdrawal.

The much-touted White House plan to hand over security to a rebuilt Afghan army and police force is widely ridiculed, and the recent atrocities have vastly complicated the already troubled negotiations between Washington and Kabul on a status of forces agreement. Anthony Cordesman, a noted conservative military analyst at the Center for Strategic and International Studies, says the Afghan army could blow apart as the United States leaves and that there has been little, if any, progress in fostering a police force and a court system. Obama wanted to be able to point to military gains, improved governance and a good start on peace talks with the Taliban when he meets with allies at the NATO summit in Chicago in May, but he’ll be able to cite none of those. More allies are likely to head for the exits, fast.

Which is precisely what Obama should do. Come September, he’ll have to announce the next phase of the drawdown, now scheduled to last through the end of 2014. The timing is propitious. In 2009 many Americans still believed the war was worth it, and it appeared that Obama acceded to his generals’ desire for more troops in order not to look weak. But today a large majority of voters want out, and if Obama accelerates the drawdown, he’ll be in sync with public opinion going into the presidential election. Even hardline GOP candidates Newt Gingrich and Rick Santorum have begun to question the viability of the occupation, though Mitt Romney continues to waffle. France has already said international forces should leave Afghanistan by 2013, and in February the New York Times reported that the Obama administration is also considering ending the US combat role next year, except for the use of Special Forces to conduct raids and train Afghan troops. But that’s not good enough. Whatever trust there was between US troops and the people they were protecting and training has long since been broken, and there is nothing for the United States to do now but leave in the most responsible way it can.