Summary: Sen. Joe Biden earns our rare Pants-on-Fire ruling with his extreme claim that President Bush is brain-dead.

During a campaign stop in Iowa on July 4, the six-term senator declared, “This guy is brain-dead.”

Rather than back away from the rhetorical excess, as other candidates might have done, Biden’s campaign posted a video of his speech on its Web site under the headline “The president is brain-dead.”

Critics of the president and the Republican Party have often used the phrase in speeches and letters to the editor. Paul Begala, a Democratic operative, once called the Bush administration “utterly and completely brain-dead.” Howard Dean, chairman of the Democratic National Committee, said in 2005 that “Republicans are brain-dead.”

Biden once used the charge against President Clinton for pardoning Marc Rich.

For the record, brain death is defined as an “irreversible unconciousness with complete loss of brain function,” according to the Encyclopedia of Death and Dying.

Needless to say, we find the charge ridiculous. Biden did not provide any material to support his medical diagnosis. We would have accepted, for instance, the results of a cerebral blood flow study or a report on whether Bush had an oculocephalic reflex.

Indeed, even people who disagree with the president about Iraq, the firing of the U.S. attorneys, commuting the sentence of Scooter Libby and assorted other issues, will acknowledge that the president has spontaneous respiration and is responding to stimuli.