Patrick Cockburn: Nixon adopted this tactic in Vietnam. It won't work any better now than it did then

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Could US Special Forces make a lunge across the Pakistan border in pursuit of the Taliban just as American and South Vietnamese troops briefly invaded Cambodia in pursuit of the Vietcong and North Vietnamese forces in 1970?

The precedent is not good. What US officers have in mind for the Pakistan border regions is much smaller in scale than President Nixon's venture, but is unlikely to be any more successful. Possible military gains are limited, while the danger of a political backlash is acute.

American frustration is great, because so long as the 2,500km Afghan-Pakistan border remains open, the Taliban can retreat to relatively safe havens to rest, re-equip and re-supply. Their fighters can recover from every tactical setback. It was this open border that prevented the Soviet army from crushing the Afghan guerrillas in the 1980s.

But would forays by US Special Forces or associated American-controlled Afghan militias really make much difference?

Even if it wanted to, the Pakistan military could hardly police a frontier through mountainous terrain that is as long as the distance from London to Moscow. Moreover the hinterland, of which the Taliban takes advantage, is not confined to the Federally Administered Tribal Areas or the border of Baluchistan. It extends into a much wider area and includes the vast city of Karachi, with its population of 17 million and sizeable Pashtun minority. The purpose of the leaks may be to intimidate the Pakistan army into being more co-operative with the US in making a ground attack on North Waziristan, seen by the US as the main redoubt of al-Qa'ida and the Haqqani network.

So far the Pakistan army has resisted this and there is no evidence it is going to change its mind.

The US often focuses its criticism of Pakistan's security policy on the ISI, Pakistan's military security agency, or even pro-Taliban "rogue elements" in it, but in practice, covert support for the Taliban is the policy of Pakistan's 600,000-strong army. Most ISI personnel are regular officers on secondment to the agency.

The White House under President Obama has long been aware that its main problem in the region is with Pakistan, but it has yet to find a way of dealing with it. Military aid – and the US pays a third of Pakistan's military budget – has produced a modicum of Pakistani compliance with US needs, though not enough to tip the balance against the Afghan Taliban.

The army has been prepared to act against the Pakistan Taliban, which it sees as being entirely different. The main military action of the US in Pakistan is through CIA-controlled drones which take off from a base in Pakistan and have been effective.

The CIA also has a 3,000-strong Afghan army of its own across the border in Afghanistan.

The drones are only as effective as the intelligence on which their targeting is based and the CIA has built up an intelligence network in border areas.

At the same time ISI officers claim privately that up-to-date information enabling the drones to attack the houses and vehicles of militants comes from them.