FIRE battalion chief Jim Riches brought up his son to be one of New York’s “bravest”, like him. The young Jim followed his father into the New York fire department and died at the World Trade Center on September 11, 2001.

What followed turned his heartbroken father into a relentless opponent of Rudy Giuliani, then mayor of New York. With other families of 9/11 victims, Riches has vowed to torpedo Giuliani’s prospects of winning the White House by attacking his greatest source of strength, his reputation as a hero that day.

“We’re going to follow him around the country,” said Riches. “We want all of America to know he is not the man he says he is.”

Helped by the firefighters’ union, Riches and his friends are preparing to “swiftboat” Giuliani, borrowing the tactics of the Vietnam veterans, under the title Swift Boat Veterans for Truth, who pierced the Democratic nominee John Kerry’s seemingly armour-plated credentials as a decorated war hero during the 2004 presidential campaign.

Republican activists have expressed reservations about whether Giuliani is truly one of them on issues such as abortion, gun control and gay rights, but they have never doubted his extraordinary standing as “America’s mayor” on 9/11. Covered in dust, issuing calm bulletins and talking reverentially about the dead and missing, Giuliani was the epitome of leadership.

If the firefighters can dent his reputation, it could be devastating for Giuliani who led John McCain, his nearest rival for the 2008 Republican nomination, by 21 points last week.

Douglas Brinkley, a biographer of Kerry, said: “Pitting the two heroes of 9/11 - Giuliani and the firefighters - against each other will be the Swift Boat campaign all over again. Giuliani has marketed himself brilliantly as the leader of 9/11 but this will damage him. Most Americans respect the firemen more than they respect him.”

Several American news organisations are preparing exposés of the “untold story” of 9/11 after Giuliani’s dispute with the firefighters became embarrassingly public last week. He was the only leading presidential candidate not to appear at a Washington gathering of the International Association of Fire Fighters, which accused him of showing a “disgraceful lack of respect for the fallen” after the September 11 attacks.

Behind the union’s attack lies the grief and anger of families who believe their loved ones need not have died that day and their conviction that some bodies would never have been recovered had Giuliani had his way.

Jim Riches, 29, had been helping to rescue office workers in the north tower when it collapsed. In the dust and debris, his fellow firefighters did not realise that the south tower had already crashed to the ground. Despite the terrifying noise, survivors say they thought only the top storeys had toppled. They never heard the order to evacuate. “My son could have had 30 minutes to escape,” Riches Sr said.

The firefighters were still using the antiquated “handie-talkie” radios that failed to work during the 1993 bombing of the twin towers, when Giuliani was also mayor. He not only failed to replace them, but also located the city’s new emergency command centre at the World Trade Center against the advice of key officials. It proved useless when it was most needed.

Lack of communication also meant that warnings from police helicopters about an imminent collapse failed to get through.

Riches was one of 343 firefighters who died. His father spent every day sifting through the wreckage for bodies, eager for some sign of his son. In November, Giuliani ordered a halt to the work after the remains of 91 firefighters had been recovered.

“Giuliani told everybody the bodies were pulverised, but I was digging them up every day. It was grisly stuff, limbs, little bones - people were blown to bits - but the bodies were there,” said Riches, 55.

The searchers refused to stop. An ugly clash between the firefighters and the New York police left 18 officers injured. Eventually Giuliani backed down and allowed the work to continue, but not before branding the firefighters’ actions as “sinful”.

As late as March, clumps of victims - 13 here, five there, a couple more scattered around - were being found. One of them was Riches’ son.

Riches Sr had taken a rare day off from ground zero to attend his grandmother’s burial when he got the call on his mobile. He raced back to help bring what remained of his son out on a stretcher draped with the American flag. If Giuliani had succeeded in closing down the operation, “I would never have got to carry little Jimmy’s body out”, Riches said. “I would never have had a cemetery to visit.”

Sally Regenhard of the Skyscraper Safety Campaign lost her firefighter son Christian, 28. She has been dogging Giuliani and the New York authorities in the courts and at public hearings, and last week was protesting outside the New York Sheraton hotel, where Giuliani was holding a fundraiser. She, too, will be hitting the campaign trail.

The firefighters’ union, which backed Kerry in the last election, will be lending its considerable resources to the fight. Well organised local chapters intend to mount their campaigns against Giuliani wherever he appears.

The threat to Giuliani comes as his position in the polls has soared, even though knowledge about his three marriages, his estrangement from his children and his liberal stance on abortion rights and gun control has spread.

He faced new challenges last week with the disclosure that his law firm, Bracewell & Giuliani, is receiving six-figure sums for lobbying Congress on behalf of Citgo Petroleum, a subsidiary of Venezuela’s state-owned oil company, despite criticism of Hugo Chavez’s regime as president.

Brinkley predicts that Giuliani will lose if he tries to face down the firefighters and their families. The answer, Brinkley believes, is to cut off the threat by apologising for some of his decisions. “He should say, ‘I just wanted to get New York moving again. I’m sorry I was insensitive’, and start talking about helping with equipment and resources,” he said.

It remains to be seen if “sorry” is in Giuliani’s vocabulary.

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