Air support and the ability to provide combat evacuations are hinged on one another, Nagl says.
"The U.S. is better than anybody in the world at providing these resources," he says. "They are expensive, complicated, technologically demanding, and the ANSF are going to have a hard time delivering [them]."
The Afghan military boasts a mixed bag of fighters, including those who are very skilled at small-unit level infantry combat, he says, as well as pilots who are comfortable in the Russian made helicopters. They lack the logistics and air support that the U.S. can offer, he adds, but so does the enemy.
Afghans are already shouldering an increasingly large portion of casualties, particularly after the announcement earlier this week that all operations are now conducted primarily by local forces, with ISAF only in a support role. Total coalition deaths dropped from 566 in 2011 to 402 in 2012, and are only 91 so far this year, according to tracking website iCasulaties.org. By contrast, the Taliban killed 1,100 members of ANSF between June 2012 and January 2013, according to the Guardian.
Nagl says the Afghans will lose fighters who could have been kept alive if the U.S. provided more medical evacuation and close air support.
But it takes months to train and integrate a fighter into a combat unit, longer than that to qualify a pilot and perhaps even more time to field the technicians necessary to maintain aircraft.
"There is no way we're going to keep the same density of medical support and medical evacuation teams that we have in the country right now," he says. "That's a real concern."
But at some point the Afghans have to stand up on their own, Nagl adds.
"With less than two years to go now to build it," Gen. Dempsey said, "the assessments that I have, and my personal observations suggest that we'll be able to make it, and have them in a position where they can do most of that, if not all of that by themselves if they have to."
The key to success is whether a central government in Afghanistan will be able to impose its will across the country, the general said, adding he will be disappointed if the Taliban is able to raise a Taliban flag over a particular district.
However, the government's ability to deploy troops to reassert control will be a sign that it is "broadly sustainable over a period of time," Dempsey said.
Upcoming peace talks, in which the Taliban raised a flag over its offices in Doha, Qatar, will be the first immediate steps toward a lasting peace in Afghanistan, says Nagl.