Why can’t we just leave Afghanistan now? It’s the unspoken question that top Pentagon officials are endeavoring to answer in their assurances that America must stay its course in the war-torn country.

It comes in the wake of a spate of “insider attacks” by Afghan security forces that have left 51 NATO service members dead this year – a 45 percent increase in such attacks over 2011.

It also comes during a month in which the surge of 30,000 forces that President Obama ordered into the country in 2009 is ending. By the end of September, some 68,000 American troops will remain in Afghanistan.

The majority of US troops are scheduled to depart in 2014, when US combat operations will come to an end.

The nation’s top military officer, Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey, stressed this week that the surge’s purpose was “to buy us some time on some Taliban initiatives,” he said, “and to buy us some space to grow the Afghan security forces.”

He says it worked, but grappled aloud with its cost. “The surge had its intended effect,” General Dempsey said. “I think it was an effort that was worth the cost – and don’t forget, it did have its cost.”

That cost continues, in both money and lives.

One American is killed every day in Afghanistan, on average, this year.

In a time of budget-cutting, the US treasury spends $60 billion a month on the war. On an annual basis, that’s enough to buy groceries for every American family for more than a year and a half.

“At some level, when you make a decision to continue waging a war, losing lives and money, you make a decision that hopefully what you can get in exchange for that is worth it,” says Stephen Biddle, professor of political science and international affairs at George Washington University and a former adviser to retired Gen. David Petraeus.

“At some point it will reach the point where what we get is no longer worth American lives.”

Analysts point out that the bulk of the war is already slated to end in 2014. After that, some American advisers will stay on the ground. But with the spate of “insider attacks” on US forces, the joint Afghan-American patrols that are a key part of the training mission have been suspended, deemed too dangerous to risk American lives.

Retired Army Maj. Gen. Paul Eaton, who commanded the Pentagon’s Iraqi security force training program from 2003 to 2004, says this latest round of green-on-blue killings will prompt tough questions among commanders and within the Pentagon. “You have to ask yourself, what has changed?” says General Eaton, now a senior adviser to the National Security Network think tank.

“Should we accelerate the cessation of combat operations from what the president laid out in the NATO conference in Chicago? These are valid questions, and that’s what [commander of US forces in Afghanistan] John Allen, his chain of command, the secretary of defense – that is precisely what they must be mulling over right now.”

Eaton and others point out that simply ending US involvement in a war is a vast undertaking, and speeding it up comes with its own risks.

Anthony Cordesman, an Afghanistan analyst at the Center for Strategic and International Studies, estimates that it will take “at least 13 months to clear the equipment we’ve got deployed. People forget that there are very real physical limits. We cannot leave the things behind at random – they’re worth too much and are potentially dangerous.”

But these are logistics, a matter in which the US military has long excelled. Troops might still guard the equipment, moving it out in an orderly manner without risking US lives. “It’s certainly isn’t true that this is something you have to continue,” Dr. Cordesman says. “You can move troops out more quickly than planned. You can cut aid more sharply.”

The larger question, he adds, is whether it is strategically desirable to leave Afghanistan now. With a focus on tamping down corruption and with a couple more years work with the Afghan national security forces, “I think what you can accomplish is a reasonable chance that the Afghan government and economy can hold together” with “some chance of a coherent structure in Kabul, and a reasonable chance that the Afghan Army can be strong enough that, with some cooperation,” it can hold insurgent forces at bay,” Cordesman says.

“Can we guarantee a future? No,” he adds. “Yes, it has been an incredibly costly and frustrating decade. And yes, we do not seem to have clear plans for the future.”

However, “We can create a situation where we can show the world that we were not defeated,” he says, and at the same time avoid a decision that would "deprive Afghanistan of any chance of stability."

“There’s a very real difference between simply running for the exits and leaving in a way that provides some chance of structure and order,” he adds.

Yet it remains an ongoing source of debate whether American forces can accomplish any more to make American any safer in the time they have left in the country – or more precisely, analysts say, whether what they might accomplish is worth any more American lives.

“The question of what we’re gaining there – that’s been a question for a number of years,” says retired Marine Col. T.X. Hammes, a senior research fellow at the National Defense University.

With Mr. Obama’s announcement of a 2014 withdrawal, “We’ve now accepted that strategically we’ve gotten all we can” out of Afghanistan. “We now have a path out that we’ve committed to,” he adds.

“We’re trying to leave, and have sufficient resources to cover our withdrawal. There’s nothing particularly ennobling in that, or anything that makes you feel good, but at least we’re leaving.”

Some military officers say, however, that as the decade-long war in Afghanistan winds down, it brings to mind Sen. John Kerry’s famous lament of Vietnam, in 1971 Senate testimony: “How do you ask a man to be the last man to die for a mistake?”

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Dr. Hammes recalls working with British forces in Iraq in 2008 “who were asking that question.” He adds that there was and is no good answer. “It’s hard for those people who are going to lose family there” in the months to come, and for the commanders and politicians who must answer for it. “That frankly is one of those leadership challenges that come with the conflict.”

Eaton recalls asking himself the same questions as a young second lieutenant in 1972, after four years at West Point, as Saigon was still raging. “The attitude was, ‘I’d really rather not be the last guy shot as we get out of Vietnam,’ ” he recalls. But “that’s been going on in warfare since we started wars – and since we’ve hoped to end them. That is part of being a soldier.”