If Mitt Romney were not a public figure, this would come pretty darn close to slander. And note that Reid himself has declined to release his own tax returns. Does that mean that he, likewise, has something to hide?
Imagine the media uproar if Mitch McConnell announced that some conveniently- unnamed source had informed him that President Obama had broken the law -- and he had repeated the unsubstantiated rumor without any knowledge of its truth. Just imagine.
Shame on the Washington Post for peddling Reid's smears without having any basis for evaluating their truth or falsehood. In my view, this comes close to journalistic malpractice.