McCain's long-time reputation as a senator with a quick temper has been raised by one Arizona newspaper and some conservative columnists.
What followed was uglier - rumors and whispers - suggesting his imprisonment as a prisoner of war in Vietnam made him unstable.
"This is very ugly stuff. It's a smear," says veteran Washington journalist Elizabeth Drew.
Drew says she has confirmed the rumors are being spread by other Republicans who have fought McCain's reform efforts.
"The issue isn't that he has a temper. We all know he has a temper. They're saying he's not qualified to be president - that he's too unstable," Drew says.
Drew says Senate Majority Leader Trent Lott and three other GOP senators - Don Nickels of Oklahoma, Robert Bennett of Utah and Paul Coverdell of Georgia - are pushing the stories. All four deny it.
McCain's military record is recognized as a political asset. The former Navy pilot was shot down over Hanoi in 1967 and thrown into prison by the North Vietnamese, where he was tortured by his captors.
Other Vietnam vets among his Senate colleagues, from both parties, have jumped to his defense.
"It's very clear that someone who is opposed to John Mccain's progress is involved in helping to push this. I think they will regret it," says Sen. John Kerry, D-Mass.
On CBS's Face The Nation, McCain admitted to a temper.
"A lot of people in New Hampshire and South Carolina are saying, 'Will you have a tantrum for me?'" McCain said.
And the senator said he plans to release all his medical records -- 350 pages. The beatings and torture, he says, made for a lot of medical paperwork after 5-1/2 years in a cell.
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