“Just a flesh wound,” exclaims the Black Knight in Monty Python’s Holy Grail to having his left and right arms hacked off by the valiant King Arthur. The Black Knight’s bravado and self-deception continue, as Arthur chops off both his legs and leaves the former a trash-talking, powerless torso with a head.

Such lack of self-awareness characterizes the coalition’s mission in Afghanistan. U.S. officials continue to praise and support the Afghan Army and police, even in the midst of a disturbing trend of Afghan security forces turning their weapons on American and NATO trainers.

This year, in nearly three dozen insider attacks, Afghan soldiers and police have killed 45 coalition troops. Nearly a quarter of all U.S. and NATO combat fatalities this year were the result of such “green on blue” attacks. It is a slap in the face to an international soldier to have to worry about being shot by those they train. The U.S. military has suspended training for some Afghan forces, but U.S. officials have pledged to keep an unspecified number of troops in Afghanistan beyond 2014 to mentor locals.

In a recent letter distributed across the service, Marines Corps Commandant General Jim Amos called the killing of coalition soldiers by Afghan forces the “carefully crafted” acts of a “desperate enemy.” A NATO study, however, finds that only a handful of attacks were the result of Taliban infiltration — angry locals with personal grievances committed between 75–90% of the killings.

What has become a “rapidly growing systemic threat,” as a classified military study warned last year, represents a “crisis of trust” long neglected and outright disputed by senior officials. Indeed, having allies of questionable loyalty remains a hazard, not only for the safety of coalition trainers but also for the future of Afghanistan.

Last spring, nearly 500 convicts escaped from a Kandahar prison in what some foreign observers alleged was an inside job. Strengthening those suspicions was the discovery of a massive tunnel constructed for months without a peep from locals or the nearby Afghan police station. At the time, the National Journal’s Yochi Dreazen pointed out that the tunnel “had fans, lighting and pre-positioned water, which is just remarkable because most Afghan construction projects that we fund don’t have that.”

President Obama added over 30,000 troops to Afghanistan in an attempt to protect the Afghan people and win their hearts and minds. On both counts, that strategy failed. More troops could not significantly suppress insurgent violence directed at the population, and a string of recent events — including the incidental burning of Qurans and the U.S. Army sergeant accused of killing 17 Afghan civilians — have jeopardized the goal to win over locals.

After eleven years, over two thousand Americans killed, and more than five hundred billion dollars spent, the Taliban remains undefeated and Afghan institutions are fragile, corrupt, and ineffectual. Consider the Afghan National Army (ANA) and police, which NATO hopes to build to 352,000 by the end of 2012, and to which Congress this year appropriated $11.2 billion to train, equip, and sustain. Jeffrey Bodin, the political and behavioral scientist working for the U.S. Army who authored the classified military study highlighted above, reported that the U.S. soldiers he surveyed in Afghanistan had “no confidence in the trustworthiness, honesty and integrity, courage or competence of ANA soldiers.”

The feeling is mutual. While some Afghan police and soldiers praised their American counterparts, many criticized them as “violent, reckless, intrusive, arrogant, self-serving, profane, infidel bullies hiding behind high technology.” In many ways, these perceptions both reflect the sentiment of many in Afghan society and influence the ANA’s ability to gain the population’s support.

Despite the opinion of his troops, General John Allen, the commander of coalition forces, described Afghan forces in recent Senate testimony as a “real defeat mechanism of this insurgency.”

In reality, Afghan security forces — and the central government they represent — look strong only on paper. Indeed, the emerging conventional wisdom is that Afghans are not ready politically or economically to take over responsibility from the international coalition. The accuracy of that assessment does not validate America’s open-ended commitment to fixing Afghanistan’s dysfunction. If anything, recent events underscore the lunacy of expending more lives, money, time, and effort to do so.

Unfortunately, much like the Black Knight, U.S. officials continue to exude a dogged persistence in the face of adversity. While such tenacity may be crucial for sustaining morale on the battlefield, it has also come to expose Washington’s refusal to accept defeat.

Incidents long described as “isolated” or “extremely rare” are more telling, routine, and extraordinary than the American people are being led to believe. Luckily, polls show that most Americans support Obama’s plan for withdrawal, and see the war in Afghanistan as not reducing the threat of terrorism. Finally, Americans have learned the right lesson from 9/11. Rather than an indefinite occupation of foreign land, a majority want to bring the troops home — as we should.