Blogger Arianna Huffington said she heard the Arizona senator and presumptive GOP presidential nominee say at a Los Angeles event after the 2000 election that he didn't vote for Bush, The New York Times reported.
The McCain campaign denied the comment, calling Huffington, a one-time Republican, "a poser" with a book to promote.
"She's a flake and a poser and an attention-seeking diva," McCain aide Mark Salter told The Washington Post.
Two other attendees -- actors Bradley Whitford and Richard Schiff -- said they heard similar comments, the Times said. McCain blamed the Bush campaign for smear tactics in the 2000 South Carolina primary.
Whitford said McCain was asked by another guest whether he voted for Bush.
"And he put his finger in front of his mouth and mouthed, 'No way,' " Whitford said.
Schiff added McCain said he was obligated "as a Republican" to support Bush's White House bid, the Times said.
"And the person said, 'Did you vote for him?' And McCain said, 'No,' " Schiff said.
Salter denied both accounts, telling the Times, "He voted for George Bush; I know it for dead certitude."