Senate Majority Leader Harry Reid (D-Nev.) has doubled (actually tripled) down on his claim that Mitt Romney did not pay taxes for 10 years.

Reid claims Romney hasn’t paid taxes (again). (Kevin Lamarque/Reuters)

“I am not basing this on some figment of my imagination,” Reid told Nevada reporters Wednesday. “I have had a number of people tell me that.” But he would not expand on his sources. “I don’t think the burden should be on me,” he said. “The burden should be on him. He’s the one I’ve alleged has not paid any taxes.”

And on the Senate floor Thursday, Reid said, “The word is out he hasn’t paid taxes for 10 years.”

“I’m telling you authoritatively speaking on the behalf of the Governor that those charges are untrue, they are baseless, and there is nothing to back them up,” said Romney adviser Eric Fehrnstrom on Fox News Thursday. Invoking Army lawyer Joseph Welch’s famous exchange with Sen. Joseph McCarthy (R-Wis.), Fehrnstrom asked, “Have you no sense of decency, sir?”

But the campaign will not release more past returns or information about Romney’s past tax rates.

Reid has a history of saying controversial things. Republicans (and some Democrats) see the tax charge as yet another example of the soft-spoken senator sticking his foot in his mouth. Jon Stewart made fun of him. Republican National Committee Chairman Reince Priebus asked if Reid had “no shame” and that it was the Democrat who had some explaining to do. Senate Minority Leader Mitch McConnell (R-Ky.) called the charge “beneath the dignity of his office.”

But this accusation is not an off-hand remark or an accident, or Reid wouldn’t be repeating it so often. He clearly sees an upside in making these claims — whether he has some proof, is trying to goad Romney into releasing the returns, or is just taking advantage of the fact that the Republican won’t prove him wrong.

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