Deep rifts at the heart of Western policy on Afghanistan were laid bare yesterday when President Obama’s top military adviser challenged him to authorise a troop surge that his most senior congressional allies have said they will oppose.

Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff, said that more US troops as well as a rapid increase in the size and capability of the Afghan army were needed to carry out the President’s own strategy for prevailing in Afghanistan as the eighth anniversary of a debilitating war approaches.

His remarks to a Senate hearing came as Bob Ainsworth, the British Defence Secretary, said that the Taleban had proven a resilient enemy. “We’re far from succeeding against them yet but I reject that we’re not making progress,” he said at King’s College London.

Mr Obama also rejected claims that Afghanistan was turning into a quagmire akin to Vietnam, but his immediate dilemma is political: approving a surge could trigger a high-level mutiny within his own party. Making matters worse, a new poll showed that public support for the war has slumped since April.

“Each historical moment is different,” Mr Obama said in an interview published yesterday. “You never step into the same river twice, and so Afghanistan is not Vietnam.”

The call for more troops is supported by military commanders and Senate Republicans, including Senator John McCain, who warned yesterday that a “wait and see” approach to a surge risked repeating the “nearly catastrophic mistakes” that the US made in Iraq.

General Stanley McChrystal, in charge of US and Nato forces in Afghanistan, is expected to make specific troop requests to add to the 68,000 already committed to Afghanistan within the next fortnight.

A central plank of his strategy, led by General Graham Lamb, of Britain, would be to try to induce low and middle-ranking Taleban fighters to fight for the Government, repeating tactics pioneered by General Lamb in Iraq two years ago, Admiral Mullen said. Britain has about 9,000 troops in the country. If he accepts his commanders’ recommendations, Mr Obama will have to remake the case for a war that had overwhelming public support until this year. He has a tough fight to persuade fellow Democrats that new troops are needed.

Democratic senators lined up yesterday to reject calls for more US combat troops. Senator Russ Feingold warned that he and “a growing chorus” of Democrats would refuse to back sending more reinforcements.

Calling for a flexible timetable for withdrawal, he insisted that “continuing to build up troops in Afghanistan is the exact formula to increase support for the Taleban”.

The argument was echoed in London by the International Institute for Strategic Studies, which warned that the continued presence of foreign troops in Afghanistan could be more destabilising than withdrawal.

Admiral Mullen’s appearance before the Senate Armed Forces Committee was ostensibly an uncontroversial renomination for two more years as America’s most senior uniformed officer. In practice, he had to walk a tightrope, defending General McChrystal’s recent assessment of the Afghan security situation while explaining his failure so far to state the number of extra troops he needs, and making the case for a surge without prejudging the decisions of his Commander-in-Chief.

“I support a properly resourced, classically pursued counter-insurgency strategy,” he told the committee. “You can’t do that from offshore and you can’t do that just by killing the bad guys. You have to be there.”

Asked by Mr McCain if the preferred Democratic solution of leaving security to a strengthened Afghan army would suffice, Admiral Mullen said: “No, sir.” Mr McCain then referred to speculation that Mr Obama had delayed tackling the issue of specific troop numbers because of the drain on his time and political capital caused by the healthcare debate. “I believe the President can do both,” his former opponent in the White House race said.

Yesterday the debate was decorous. It is likely to turn acrimonious in the weeks ahead as Republicans train their fire on delays that they will argue have put American lives at risk.

When Admiral Mullen revealed that General Lamb had initiated an effort to win over Taleban fighters, he was asked why it had taken so long. “It has not been an area of focus,” he said.

Asked how the Taleban could have the initiative against the world’s most powerful military despite having no tanks or aircraft, the admiral replied: “They’re very good at it. It’s their country. They know how to fight.”

Senator Lindsey Graham, one of an influential cross-party trio likely to frame the congressional response to Mr Obama’s next move on Afghanistan, alluded to a new CNN poll showing a 14 per cent drop in public backing for the war. He asked Admiral Mullen: “Do you understand that you’ve got one more shot back home?” The admiral said that he did.

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