The United States risks “snatching defeat from the jaws of something that could still resemble victory” if it speeds up its withdrawal from Afghanistan and fails to make long-term financial and military investments in the country, according to a new report co-authored by a former U.S. military commander there.

The report, written by retired Marine Gen. John R. Allen, former undersecretary of defense Michèle Flournoy and defense analyst Michael O’Hanlon for the Center for a New American Security, calls on Washington and Kabul to clarify as soon as possible the size of an ongoing U.S. military presence in Afghanistan after combat troops withdraw at the end of next year.

“This would reduce incentives for hedging behavior in Afghanistan and Pakistan and contribute to a constructive atmosphere for the campaigns leading up to the crucial April 2014 Afghan presidential election,” they wrote.

The report disputes critics who consider the Afghan war a “lost cause,” but acknowledges that the U.S. mission has achieved only partial results and has been plagued by Afghan corruption, a fickle ally in Pakistan and a resilient enemy in the Taliban.