"With a single bound, our hero was free", as writers of pulp fiction used to say when they saved their hero from some implausible but inescapable peril. Barack Obama could now free himself from Afghanistan with a single bound, if he had the nerve.

The death of Osama bin Laden, founder of al-Qaeda, matters little in practical terms, but Obama could use it as a means of deflating the grossly exaggerated “terrorist threat” that legitimises the bloated American security establishment. He could also use it to escape from the war in Afghanistan.

If he acted in the next few months, while his success in killing the terrorist-in-chief still makes him politically unassailable on military matters, he could start moving U.S. troops out of Afghanistan, and even begin to cut the Homeland Security Department down to size. His political enemies would accuse him of being “soft on defence”, but right now the accusation would not stick.

The HSD's reason for being is the “terrorist threat”. Drive home the point that bin Laden is dead, and that there has been no terrorist attack in the West at even 1/50 the scale of the 9/11 attacks for the past five years, and its budget becomes very vulnerable.

Obama promised in 2009 that the first of the 30,000 extra U.S. troops he sent to Afghanistan in that year will be withdrawn this July. It would be harder to get the remaining 70,000 American troops and the 50,000 other foreign troops out—but it is now within his reach.

Since it is politically impossible for a U.S. president to acknowledge military defeat, for half a century the default method for extracting American troops from lost wars has been to “declare a victory and leave”. It was pioneered by Henry Kissinger in the Vietnam era, it worked for the junior Bush in Iraq, and Obama could use it to get out of Afghanistan.

It just has to look like a victory of sorts until one or two years after all the American troops are gone, so that when the roof falls in, it no longer looks like the Americans’ fault. Kissinger talked about the need for a “decent interval” between the departure of U.S. troops and whatever disasters might ensue in Vietnam, and the concept applies equally to Obama and Afghanistan.

The case for getting Western troops out of Afghanistan now rests on three arguments. Firstly, that the Taliban, the Islamist radicals who governed the country until 2001 and are now fighting Western troops there, were never America’s enemies. Al-Qaeda (which was almost entirely Arab in those days) abused their hospitality by planning its attacks in Afghanistan, but no Afghan has ever been involved in a terrorist attack against the West.

Secondly, the Taliban never controlled the minority areas of the country even during their five years in power, so why assume that they will conquer the whole country if Western troops leave? President Hamid Karzai’s deeply corrupt and widely hated government would certainly fall, but Afghanistan’s future would probably be decided, as usual, by a combination of fighting and bargaining between the major ethnic groups.

And thirdly, Western troops will obviously leave eventually. Whether they leave sooner or later, roughly the same events will happen after they go. Those events are unlikely to pose a threat to the security of any Western country—so why not leave now, and spare some tens of thousands of lives?

This last argument is of course disputed by the U.S. military, who insist (as soldiers usually do) that victory is attainable if they are only given enough resources and time. But Karzai’s government is beyond salvage, and this month’s strikingly successful Taliban attacks in Kandahar city discredit the claim that pro-government forces are “making progress” in “restoring security”.

Western armies have fought dozens of wars in the Third World since the European empires began to collapse 60 years ago, and they lost almost every one. The local nationalists (who sometimes calling themselves Marxists or Islamists) cannot beat the foreign armies in open battle, but they can go on fighting longer and take far higher casualties.

Afghanistan fits the model. When a delegation from Central Asia visited a U.S. base in Afghanistan, one of the delegates was a former Soviet general who had fought in Afghanistan during the Soviet occupation in the 1980s. He listened patiently as eager young American officers explained how new technology and a new emphasis on “winning hearts and minds” would defeat the insurgency.

Finally his patience snapped. “We tried all that when we were here and it didn’t work then, so why should it work now?” he asked. Answer: it won’t.

Osama bin Laden’s death has given Obama a chance to leave Afghanistan without humiliation. Just wait a couple of months to guard against the improbable contingency of a big terrorist revenge attack, and then start bringing the troops home. Once the Taliban are convinced that he is really leaving, they would probably even give him a “decent interval".

Will this actually happen? Probably not, for in terms of domestic U.S. politics it would be a gamble, and Barack Obama is not a gambler.