When President George W. Bush invoked the memory of Vietnam to justify staying in Iraq, he was drawing on a new wave of revisionist history, which maintains that America did not lose the war, but the will to win.

“Three decades later there is a legitimate debate about how we got into the Vietnam war and how we left,” Bush said in a speech to army veterans last week. White House insiders admitted it was a risky topic which had previously been left to the anti-war movement. Americans generally prefer to forget Indochina and remember who won the Cold War.

Yet as the prospect of victory in Iraq has receded, the lessons of Vietnam have provoked intense discussion among historians and in current affairs magazines such as the neo-conservative Weekly Standard.

Bush has been quietly paying attention and had been thinking for months about the right moment to bring Vietnam into the debate, according to a White House official.

In "Triumph Forsaken," published last year, the historian Mark Moyar claimed that South Vietnam could have survived had the Americans not acquiesced in the overthrow of President Ngo Dinh Diem in 1963, plunging the country into an “extended period of instability and weakness.”

Moyar is now working on a book about the second half of the war, in which he argues: “In the offensive of 1975, the North Vietnamese are moving around huge conventional forces that would have been pulverised by our air power.” By then, however, Hanoi was well aware that America was turning against the war and doubted that the U.S. military would be able to act decisively.

Supporters of the Iraq war have also been delving into Lewis Sorley’s book,"A Better War," which was re-released in paperback this year. The war, Sorley wrote, “was being won on the ground even as it was being lost at the peace table and the U.S. Congress.”

The North Vietnamese have given this argument a boost over the years. In an interview after his retirement, Bui Tin, who received the South Vietnamese army’s unconditional surrender in 1975, recalled that visits to Hanoi by Jane Fonda, church ministers and other anti-war protesters “gave us confidence that we should hold on in the face of battlefield reverses ... through dissent and protest [America] lost the ability to mobilize a will to win”.

James Q. Wilson, a social scientist who is revered by conservatives, argued in The Wall Street Journal last year: “Whenever a foreign enemy challenges us, he will know that his objective will be to win the battle ... among the people who determine what we read and watch. We are in danger of losing in Iraq ... in the newspapers, magazines and television programs we enjoy.”

Anti-war historians have hit back at Bush’s invocation of Vietnam. “What is Bush saying?” asked Robert Dallek, the biographer of John F. Kennedy and Lyndon Johnson. “That we didn’t fight hard enough, stay long enough? That’s nonsense.”

The debate is not just academic for Sen. John Warner, former chairman of the Senate Armed Services Committee, who called last week for Bush to begin pulling out 5,000 troops from Iraq by Christmas. The 80-year-old Republican is still haunted by the memory of Vietnam.

“The army generals would come in [and say], ‘Just send in another 5,000 or 10,000,’” Warner recalled. “You know, month after month. Another 10,000 or 15,000. They thought we could win it. We kept surging in those years. It didn’t work ... You don’t forget something like that.”

Senior generals, including Peter Pace, chairman of the joint chiefs of staff, and George Casey, the army chief of staff, are believed to support reducing the number of U.S. troops in Iraq to below 100,000 by the end of next year.

Defense Secretary Robert Gates is also thought to favor the idea of drawing down 3,500 soldiers every other month or so and accelerating the pace after April, when troop shortages will make the surge impossible to sustain at current levels.

However, Gen. David Petraeus, the U.S. commander in Iraq, is likely to demand more time for the surge to work when he reports to Congress on the progress of the war next month. Last year, in his previous job as head of the army college at Fort Leavenworth in Kansas, he made a point of examining the “lessons learnt” from the Vietnam war.

One lesson was that it takes time to “clear and hold” communities and build a political settlement. Major-Gen. Rick Lynch, who is based south of Baghdad, said on Friday that pulling out American troops would allow Sunni and Shi’ite fighters to regroup within 48 hours.

The enemy would start “building the bombs again ... and we would take a giant step backwards,” he said.

Ultimately, Iraq could experience the maelstrom that overtook Vietnam and Cambodia. “One unmistakable legacy of Vietnam,” Bush warned last week, “is that the price of America’s withdrawal was paid by millions of innocent citizens whose agonies would add to our vocabulary new terms like ‘boat people,’ ‘re-education camps’ and ‘killing fields.’”

A humanitarian disaster on this scale would cast a pall over Bush’s decision to invade Iraq. It may be some comfort to him to imagine that, 30 years on, intellectuals may launch a revisionist movement that would look more kindly on his war record.