Former New York mayor and presidential hopeful Rudolph Giuliani gained fame for his performance after the September 11 attacks, but charges that he also made serious blunders could give ammunition to rival candidates.
Mr Giuliani, a Republican, has all but formally declared his candidacy and polls show he is a strong contender, largely because of his steely and comforting leadership that day in 2001.
But Mr Giuliani also made mistakes in handling the city's emergency services that may have cost lives, say the co-authors of the 2006 book "Grand Illusion: The Untold Story of Rudy Giuliani and 9/11."
Of the 2,992 people killed in the hijacked plane attacks, 2,759 died at New York's World Trade Center.
Such criticism raises the possibility the former mayor may be attacked on his perceived strength, as 2004 Democratic nominee John Kerry was when his Vietnam War record was called into question.
A Giuliani aide defended his performance, noting that 25,000 people were safety evacuated from the danger zone.
The Giuliani campaign is more concerned about attacks on his personal life, including his three marriages, and support for gay rights and abortion rights could also alienate social conservatives crucial to the winning the Republican nomination.
"Clearly if you want to take Rudy Giuliani down or out you've got to go after 9/11 but it's going to be a tough job to deconstruct that heroic narrative," said Doug Muzzio, public affairs professor at New York's Baruch College.
"There is a lot that went on that day and prior that if fully known would tarnish the mythology of 'America's Mayor,'" Muzzio said, using a nickname some have attached to Giuliani. "Grand Illusion," written by two journalists, says that in the late 1990s Giuliani went against the advice of police and emergency management experts and placed the city's emergency command centre in the World Trade Center complex, which had been bombed in 1993 and was a presumed future target.
The command centre had to be abandoned on September 11, 2001, after hijacked planes slammed into two skyscrapers next door.
In the chaos that ensued Mr Giuliani allowed fire and police commanders to be separated in violation of the city's own protocols, co-authors Wayne Barrett and Dan Collins say.