We should stop looking at the withdrawal as an operation designed to bring Americans home with little regard for what's left behind.

In one of his first major statements on Afghanistan as Secretary of Defense, Chuck Hagel defined America's "clear and achievable" objective in Afghanistan: "to have Afghans assume full responsibility for security by the end of 2014." America's core aim has narrowed dramatically: to hand over power and withdraw.

The new goal is certainly clear and achievable. Indeed, the United States could accomplish Afghan responsibility right now, simply by leaving. The danger is that the mission turns into what Gideon Rose once called a "moon landing," or an operation designed to transport Americans far away and bring them home safely with little regard for what's left behind.

Hagel's comment captures the evolution in U.S. war aims in Afghanistan away from building a stable country and defeating the Taliban to getting out, "come hell or high water" as Joe Biden once put it.

Back in 2009, Obama nearly tripled U.S. forces in Afghanistan and adopted an expansive counter-insurgency strategy. At one meeting in November 2009, Obama turned to General David Petraeus and said, "What I'm looking for is a surge."

But the president soon became disillusioned by the slow pace of change in Afghanistan and searched for a quicker exit strategy. Obama's disenchantment is part of a wider depression system drifting over the American landmass. Republicans from John Huntsman to Newt Gingrich and Mitt Romney are sick and tired of the war. Public enthusiasm for the campaign is down to a kettle of hawks that would probably back an invasion of Canada.

In 2010, the president formed a committee -- known as "Afghan Good Enough"-- to narrow the scope of the mission away from nation-building toward defeating Al Qaeda -- thereby allowing most U.S. troops to withdraw by 2014.

This brings us to Hagel, and an even narrower goal: handing over responsibility to Kabul. To be fair, the secretary of defense added that the mission "will help ensure that al Qaeda does not re-establish the safe haven they had before September 11, 2001," and also, "help forge a more peaceful future for the people of Afghanistan, for the region, and--in turn--for the world." But these appear less as core American objectives, and more as hoped-for byproducts of an exit plan singularly focused on relinquishing responsibility.

If we're not careful, the exit strategy will be more about exit than strategy. The aim of war is not to leave, but instead to achieve political goals--to decide who rules and how. In other words, we must use our limited resources and time to create a tolerable political outcome on the ground. Focusing on the handover of responsibility dodges the tough questions. What do we want Afghanistan to look like at the end of 2014? Are we aiming for a peace deal with the Taliban? Is the handover set in stone or is there any wiggle room depending on the state of the country?

After a decade of fighting, the war in Afghanistan is too costly to be considered a success. But many outcomes are still possible, from a stalemate with some hope of progress, to a catastrophic disintegration of the country that threatens neighboring Pakistan. No one wants a massive and prolonged commitment of U.S. forces, but a relatively modest effort may be the difference between a draw and a defeat.

A critical issue, for example, is the size of the follow-on American force that remains in Afghanistan after 2014. The outgoing head of U.S. Central Command General James Mattis recommended that around 13,600 U.S. troops stay on. But the final figure may be only half as large. Some have floated the idea of leaving entirely.

We've gone from writing a blank check to nickel-and-diming the mission. In practical terms, the follow-on force will play an important role with advising and counter-terrorism. In psychological terms, it will be a statement of the continued American and allied commitment to Afghanistan.

To suddenly leave sends a signal that the Taliban is winning. This could produce a tipping point, or a rapid and unexpected negative turn in the war, as local allies defect, fence sitters jump over to the insurgent side, civil servants stop coming to work, and investors abandon a sinking ship.

Vali Nasr writes in the latest Foreign Policy that Obama is fast "washing his hands" of the Afghanistan War. Getting American troops home safely is obviously vital. But it's not the primary purpose of the mission. We don't want a moon landing. After all, the moon today is a dusty and arid land where the harsh atmosphere has bleached American flags into white pennants.