For the first time on Thursday, Mitt Romney addressed Senate Majority Leader Harry Reid's claim that Romney spent a decade not paying taxes, denying the charge and telling Fox News' Sean Hannity that it was time for the majority leader reveal the source of his information.

"Well, it's time for Harry to put up or shut up. Harry's going to have to describe who it is he spoke with because of course, that's totally and completely wrong," Romney told Hannity in a radio interview. "It's untrue, dishonest, and inaccurate. It's wrong. So I'm looking forward to have Harry reveal his sources and we'll probably find out it's the White House. Look, the Obama campaign is going to do everything in its power to try and talk about anything besides the president's record. Home prices, median American incomes, gasoline prices, 23 million underemployed or unemployed.

"They don't want to talk about that or his promises, cutting the deficit in half, cutting the medical insurance rates that people pay," Romney added. "These are all the things he promised. He can't talk about that, so they try and put this kind of baloney out there, and the people could smell it for what it is, and it's not a pretty smell."

Democrats were quick to wonder why Romney would even engage Reid on the matter, adding another chapter to this bizarre squabble. But that's not particularly fair to the presumptive Republican nominee, who was asked a direct question about the Reid's insistence that an anonymous investor in Bain Capital told him about Romney's zero tax bill.

That said, the put-up-or-shut-up line works both ways. Romney could make the whole issue go away (and make Reid look foolish in the process) by simply releasing more tax returns. The campaign showed no willingness to do that, especially under the terms that Reid's established. But that seems likely to just invite even more speculation.

UPDATE: 8:46 p.m. -- Reid is not backing down. He put out a statement Thursday night declaring that his source at Bain (who he said told him about Romney not paying taxes) is "extremely credible" and insisted that the one way to clear up the matter is for Romney to be more transparent.

There is a controversy because the Republican presidential nominee, Governor Mitt Romney, refuses to release his tax returns. As I said before, I was told by an extremely credible source that Romney has not paid taxes for ten years. People who make as much money as Mitt Romney have many tricks at their disposal to avoid paying taxes. We already know that Romney has exploited many of these loopholes, stashing his money in secret, overseas accounts in places like Switzerland and the Cayman Islands.

Last weekend, Governor Romney promised that he would check his tax returns and let the American people know whether he ever paid a rate lower than 13.9 percent. One day later, his campaign raced to say he had no intention of putting out any further information.

When it comes to answering the legitimate questions the American people have about whether he avoided paying his fair share in taxes or why he opened a Swiss bank account, Romney has shut up. But as a presidential candidate, it’s his obligation to put up, and release several years’ worth of tax returns just like nominees of both parties have done for decades.

It’s clear Romney is hiding something, and the American people deserve to know what it is. Whatever Romney’s hiding probably speaks volumes about how he would approach issues that directly impact middle-class families, like tax reform and the economy. When you are running for president, you should be an open book.

I understand Romney is concerned that many people, Democrats and Republicans, have been calling on him to release his tax returns. He has so far refused. There is only one thing he can do to clear this up, and that’s release his tax returns.

Also on HuffPost:

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  • Ron Paul

    "Politically, I think that would help him," Paul said in a interview with <a href="http://www.politico.com/news/stories/0712/78599.html#ixzz20w7ycTBE" target="_hplink">Politico</a>. "In the scheme of things politically, you know, it looks like releasing tax returns is what the people want."

  • Richard Lugar

    "I have no idea on why he has restricted the number to this point," <a href="http://www.cbsnews.com/8301-18563_162-57474352/pressure-mounts-on-mitt-romney-to-release-more-tax-returns/?tag=socsh" target="_hplink">Lugar said</a>.

  • George Will

    "I don't know why... he didn't get all of this out and tidy up some of his offshore accounts and all the rest," Will said on ABC's "<a href="http://www.huffingtonpost.com/2012/07/15/george-will-mitt-romney-bain_n_1674513.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+HP%2FPolitics+(Politics+on+The+Huffington+Post)" target="_hplink">This Week</a>." "He's done nothing illegal, nothing unseemly, nothing improper, but lots that's impolitic."

  • Bill Kristol

    "He should release the tax returns tomorrow. It's crazy," Kristol said on "<a href="http://www.huffingtonpost.com/2012/07/15/mitt-romney-tax-returns_n_1674325.html" target="_hplink">Fox News Sunday</a>." "You gotta release six, eight, 10 years of back tax returns. Take the hit for a day or two."

  • Robert Bentley

    "I just believe in total transparency," Bentley told <a href="http://abcnews.go.com/blogs/politics/2012/07/gop-governor-calls-on-mitt-romney-to-release-additional-tax-returns-and-show-he-has-nothing-to-hide/" target="_hplink">ABC News</a>. "In fact, I was asked today that question -- do you think that Governor Romney should release his tax returns? And I said I do. I said, I release my tax returns. I may be the only public official in Alabama that does, but I release mine every year and I just believe that people should release their tax returns. And if you get them out and just get past that, it just makes it so much easier."

  • Haley Barbour

    When asked on "<a href="http://www.nationaljournal.com/2012-presidential-campaign/barbour-romney-should-release-more-tax-returns-20120710" target="_hplink">The Situation Room</a>" if Romney should release more returns, Barbour said, "I would. But should it be an issue in the campaign? I don't think it amounts to diddly."

  • Michael Steele

    "If there's nothing there, there's no 'there' there, don't create a there,'" Steele said on MSNBC.

  • David Frum

    "Tax returns the next problem. Releasing returns under pressure: more weakness, more pain," Frum <a href="https://twitter.com/davidfrum/status/224509505973661696" target="_hplink">tweeted</a>.