A concerted assault this week on the leadership character of John Kerry may have done more to smear the reputation of his assailants than the Democratic presidential candidate.
A group of Vietnam veterans funded by a wealthy Republican donor has launched a campaign questioning his valour.
The television advertisements follow last month's Democratic National Convention, which highlighted Mr Kerry's military service in Vietnam as proof of his readiness to serve as America's next commander-in-chief.
By Friday, the attack appeared to be backfiring, as new questions arose over the accuracy of the allegations, and the Bush campaign found itself exposed to criticism for failing to condemn dirty politics.
John McCain, the Republican senator from Arizona known for spending more than five years in aVietnamese prison camp, angrily defended Mr Kerry's reputation and attacked the advertisement's self-styled “Swift Boat Veterans for Truth”.
“I deplore this kind of politics,” Mr McCain said. “I think this ad is dishonest and dishonourable.”
Mr McCain called on the White House and the Bush-Cheney campaign to condemn the adverts.
The president's re-election team issued a statementthat stopped short of outright condemnation: “The Bush campaign has never questioned John Kerry'sservice in the militaryand we never will.”
“It was the same kind of deal that was pulled on me,” Mr McCain said, referringto the vicious 2000Republican presidential primary campaign in South Carolina against George W. Bush, who was then governor of Texas.
Anonymous opponents of Mr McCain, posing as pollsters, had called voters suggesting the senator had an illegitimate black child.
Mr McCain, who has two adopted daughters of Bangladeshi origin, subsequently lost the South Carolina primary to Mr Bush.
Democrats point out that Robert J. Perry, the group's primary financial backer, is a Houston-based contributor to Republicans in Texas, though not officially tied to the Bush-Cheney re-election efforts.
Adding to questions over the veracity of the accusations, one of the leading figures in the group of accusers reportedly recanted on a statement alleging that Mr Kerry lied and “had simply shot a wounded fleeing Viet Cong in the back”.
This constituted one of the key claims of a book Unfit for Command: Swift Boat Veterans speak out against John Kerry which isdue to be publishednext week.
George Elliott, who had been Mr Kerry's commanding officer, told the Boston Globe this week that it was “a terrible mistake” to sign the affadavit in those words. But after the story appeared, the group claimed that the report misstated Mr Elliott's views.
The newspaper on Friday said it stood by its account.