A new ad released by the Obama campaign Thursday suggests that Mitt Romney might have paid nothing in taxes at some point. The ad plays a clip of a recent interview in which Romney said he was "happy to go back and look" to see if he had paid a rate lower than 13.9 percent -- but he never did get back to the voters on that.

"Did Romney pay 10 percent in taxes? 5 percent? Zero?" asks a narrator. "We don’t know."

The campaign says the ad is "following" Romney through Virginia, North Carolina, Florida and Ohio next week.

Senate Majority Leader Harry Reid (D-Nev.) recently ignited a firestorm of criticism by saying, in an interview with The Huffington Post, that a Bain investor had told him that Romney paid no taxes for 10 years. The presumptive GOP nominee has refused to release his tax returns for the years before 2010 despite bipartisan calls for him to do so.

Related 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>.