I just got off the phone with Huntsman, and he confirmed to me that he is not Reid’s source.

However, in a move that could be significant, Huntsman forcefully called on Romney to release his tax returns. This matters, because Huntsman is a longtime backer of Romney — he has long been close to Romney; he supported his early campaigns; he was the national finance chairman of Romney’s 2008 presidential campaign; and he has raised a lot of money for him over the years. (He backed his own son in the latest GOP primary.)

“I feel very badly that Mitt won’t release his taxes and won’t be fair with the American people,” Huntsman told me. In a reference to Romney’s father, who pioneered the release of returns as a presidential candidate, Huntsman said: “I loved George. He always said, pay your taxes for at least 10 or 12 years.”