The appropriate question is not whether the war is winnable. If we define victory narrowly, if we are willing to apply the resources necessary to have a reasonable chance of success, and if we have capable and credible partners, then of course the war is winnable. Any war is winnable under these conditions.

None of these conditions exist in Afghanistan, however. Our mission is too broadly construed. Our resources are constrained. The patience of the American people has worn thin. And our Afghan partners are unreliable and unpopular with their own people.

Given this, the better question is whether the resources that we have already ploughed into Afghanistan, and those that would be required in the medium to long term, could be better spent elsewhere. They most certainly could be.

More important still is the question of whether the mission is essential to American national security interests — a necessary component of a broader strategy to degrade al-Qaeda’s capacity for carrying out another terrorist attack in America. Or has it become an interest in itself? (That is, we must win the war because it is the war we are in.)

Judging from most of the contemporary commentary, it has become the latter. This explains why our war aims have expanded to the point where they are serving ends unrelated to our core security interests.

The current strategy in Afghanistan is flawed. Population centric counterinsurgency (COIN) amounts to large-scale social engineering. The costs in blood and treasure that we would have to incur to accomplish this mission — in addition to what we have already paid — are not outweighed by the benefits, even if we accept the most optimistic estimates as to the likelihood of success.

It is also unnecessary. We do not need a long-term, large-scale presence to disrupt al-Qaeda. Indeed, that limited aim has largely been achieved. The physical safe haven that al-Qaeda once enjoyed in Afghanistan has been disrupted, but it could be recreated in dozens of other ungoverned spaces around the world — from Pakistan to Yemen to Somalia. The claim that Afghanistan is uniquely suited to hosting would-be terrorists does not withstand close scrutiny.

Nor does fighting terrorism require over 100,000 foreign troops building roads and bridges, digging wells and crafting legal codes. Indeed, our efforts to convince, cajole or compel our ungrateful clients to take ownership of their problems might do more harm than good. Building capacity without destroying the host nation’s will to act has always proved difficult. This fact surely annoys most Americans, who have grown tired of fighting other people’s wars and building other people’s countries. It is little surprise, then, that a war that once enjoyed overwhelming public support has lost its lustre. Polls show that a majority of Americans would like to see the mission drawn to a close. The war is even less popular within the European countries that are contributing troops to the effort.

You go to war with the electorate you have, not the electorate you wished you had. But while the public’s waning appetite for the war in Afghanistan poses a problem for our current strategy, Hamid Karzai poses a greater one. Advocates of COIN explain ad nauseam that the success of these missions depends upon a reliable local partner, something that Mr Karzai is not. Efforts to build support around his government are likely to fail. An individual who lacks legitimacy in the eyes of his people does not gain from the perception that he is a foreign puppet. Mr Karzai is caught in a Catch-22. His ham-fisted efforts to distance himself from the Obama administration have eroded support for him in America without boosting his standing in Afghanistan.

America and its allies must narrow their focus in Afghanistan. Rather than asking if the war is winnable, we should ask instead if the war is worth winning. And we should look for alternative approaches that do not require us to transform what is a deeply divided, poverty stricken, tribal-based society into a self-sufficient, cohesive and stable electoral democracy.

If we start from the proposition that victory is all that matters, we are setting ourselves up for ruin. We can expect an endless series of calls to plough still more resources — more troops, more civilian experts and more money, much more money — into Afghanistan. Such demands demonstrate a profound misunderstanding of the public’s tolerance for an open-ended mission with ill-defined goals.

More importantly, a disdain for a focused strategy that balances ends, ways and means betrays an inability to think strategically about the range of challenges facing America today. After having already spent more than eight and a half years in Afghanistan, pursuing a win-at-all-costs strategy only weakens our ability to deal with other security challenges elsewhere in the world.