Reid, who refuses to release his own tax returns, has refused to provide proof of his Romney tax claim and hasn’t revealed the identity of the person who allegedly gave him the information. Nor did he explain how someone who invested in Bain, which was Romney’s firm, would know the details of Romney’s personal income taxes.

Some experts on political language and civility said they were aghast that someone in the political leadership of the country – not a bomb-throwing back-bencher – would level such a serious charge without providing any proof.

“He shouldn’t be making statements like that in public. If you do, produce the evidence or produce the person (who provided the information) in public,” said Kathleen Hall Jamieson, director of the University of Pennsylvania’s Annenberg Public Policy Center and co-founder of FactCheck.org, a political fact-checking Website.

“We need a new category to define inappropriate content. ‘Hearsay’ is good. What he (Reid) said would not be admissible in court as evidence,” she said.

Carolyn Lukensmeyer, executive director of the nonpartisan National Institute for Civil Discourse at the University of Arizona, said Reid’s remarks are indicative of “a level of insinuating character assassination” that’s becoming all too common in today’s politics.

“We’re actually degrading our institutions,” she said. “It’s incumbent on the political parties to back up what they said.”