(CNN) - Mitt Romney on Thursday pushed back against Senate Majority Leader Harry Reid's allegations that the presumptive GOP nominee has not been paying his taxes.
"It's time for Harry to put up or shut up," Romney said on Sean Hannity's radio show.
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In a Huffington Post interview published Tuesday, the leading Democrat said that an unnamed investor with Bain Capital, Romney's former private equity firm, told Reid in a phone conversation that Romney had not paid taxes for a decade.
Reid stood by the allegations on Thursday while speaking on the Senate floor.
"The word's out that he hasn't paid any taxes for 10 years," he said. "Let him prove he has paid taxes because he hasn't."
Democrats and President Barack Obama's re-election campaign have repeatedly called for Romney to release more tax documents to answer any questions about his financial portfolio.
Romney has made public the full 2010 tax return and an estimate for 2011, with a pledge to release the full year once it's complete. He filed an extension for an October deadline.
Critics have hit back against Reid's comments this week, faulting him for making claims based off an anonymous source.
"Harry's gonna have to describe who it is he spoke with because of course that's totally and completely wrong," Romney said Thursday in the 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 that it's the White House."
Mirroring Romney's comments, senior campaign adviser Eric Fehrnstrom described Reid's comments as "shameful, pathetic, baseless and untrue" and argued the majority leader, with the help of the Obama campaign, was attempting to "engage in McCarthy-like accusations about Mitt Romney."
"Four years ago Barack Obama said he was going to come to Washington and change the politics. Instead the Obama campaign has turned into a bottomless pit. Every day they reach a new low," he said Thursday on CNN's "The Situation Room."
Adding on, Fehrnstrom said Romney has "never zeroed out his tax liability" and "has always paid 100% of what was owed."
After Romney's interview on Hannity's radio show, the majority leader responded in a statement and said he is not backing down from his remarks.
"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 Romney have many tricks at their disposal to avoid paying taxes," he said.
Reid argued Romney is "hiding something" and called on the presumptive GOP nominee to release more taxes.
"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," Reid said.
According to a source familiar with Reid's thinking, the majority leader, a former boxer, considers himself a political street fighter now, willing to throw a punch and get hit back big time for a cause. In this case, the cause is making sure the topic of Romney's tax returns remains in the news, and in the campaign narrative.
The source said Reid is "happy to mix it up and put this back in the news" and added the "finger waggers of the Acela corridor won't dissuade him from speaking his mind."
Reid, the source said, is unconcerned about the hits he is taking on making unsubstantiated claims, because the Democratic base is fired up. The source says they know that anecdotally. It's not an accident that Reid said this to the Huffington Post, a friendly outlet, and did so as Romney was returning from his overseas trip.
"What happened when Romney returned? The first story he has to deal with is his tax returns," the source said.
One of Romney's biggest surrogates, Sen. John McCain of Arizona, came to Romney's defense on Thursday, saying Reid may have "gone over the line."
"I've known Sen. Reid for many, many years, and occasionally he displays some rather erratic behavior," McCain said on CNN's "Anderson Cooper 360." "To accuse someone of doing something without a shred of proof–that the allegation has any substance–is really something I, frankly, don't understand."
McCain, whose 2008 presidential campaign reviewed Romney's tax records as they considered him to be the vice presidential running mate, said last month he can "personally vouch" that there was "nothing disqualifying" in the tax returns of the presumptive GOP presidential nominee.
On Thursday, he urged Reid to come "forward" with his source.
"I think politics are tough. I enjoy the give and take but I think Harry might have gone over the line," McCain said.
Later, while visiting a fruit stand with his mother in Florida, Ryan responded to the negative reaction in the room.
"Entitlement reform has unfortunately been made very partisan by partisans, and so I have gotten that kind of reaction and unfortunately it's what we come to expect because the politics of reforming entitlements has become very bitter and it's very unfortunate," he told reporters in Lakeland.
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Good for Romney....Romney is not to be underestimated.
Reid said , it's out there, but it's unsubstantiated.....so where's the proof Reid.
It's true that Romney didn't pay taxes for 10 years! ... (1947 – 1957)
Really, Willard. YOU need to put up or shut up...Where are your taxes? Prove America wrong...I dare you..
"... any taxes for 10 years." Which ten years, Mr Reid? Since the 2010 tax records are publicly available, do we assume you mean 10 years not including 2010? Perhaps your illustrious source would like to provide more specific information?
Well, Mitt could sure put a stop to these rumours by having a show and tell session. I thought those running for political office, especially the top office would know they had to show they pay taxes like everyone else.
Perhaps Senator Reid should pay his fair share of taxes on profits he made from the bridge he constructed on his own land.
I'd like to see Harry Reid's tax returns for the last ten years and how he handled his land deals.
Romney needs to release his tax returns. Romney says, I will follow the precedent established by John McCain and release just two years. Newsflash Romney: He lost. McCain's campaign did not work so why on earth would you follow that example?
one more comment, romney saying put up or shut up is pretty funny. well romney, put up or shut up!
Romney needs to release his tax returns. Romney says, I will follow the precedent established by John McCain and release just two years. Newsflash Romney: He lost. McCain\'s campaign did not work so why on earth would you follow that example?
No, mittens, its time for you to release your tax returns... and stop trying to hide as much of the millions you make for doing nothing from the tax man. Its patriotic to actually pay your taxes, especially when you can so easily afford it.
Well Mitt, why don't you just release your taxes and prove Reid wrong ... oh that's right, you don't want anyone to see what's in your taxes.
I haven't asked for Mitt to release his tax records, but I would love to see him do it now and then sue Reid for slander!
Actually it is Romney who needs to "put up or shut up" Because he has unwisely chosen to hide his tax returns there is all kinds of speculation out there about what he may be hiding. This is just one allegation. Sen. Reid said he didn't know if it was true but it is quite possible isn't it? Romney has brought this on himself and it is going to dog him to election day.. The speculation may be worse than the facts so he should just reveal the last ten years like others have done and get it over with.
Oh, Mitt..careful what you ask for. You have been caught sooo many times telling lies.
Dem lies! He release his 2010 return that showed he paid taxes for that year. The rest is just another smear.
Just release the incom tax returns Mittens.
Romney says "Put up or shut up" huh? Well, Mitt, put up your tax returns or shut up about the obvious conclusion when you don't.
Well, well!!! Let's start with Barry Sotero posting his school records, Pelosi and Reed posting THEIR 10 year tax returns – all in the former main stream media. Of course they won't because they don't want the democrat voters to know how rich they are and what a double-standard they practice.
Why don't they both release their tax returns?
Harry Reid represents all that is wrong with this Country!
Maybe Romney should reply with "I'll show my tax records after you've passed a budget."
In America if you make billions your income is not taxable – if you make the minimum hourly wage your income is fully taxable. No wonder its bridges are falling down.
No Mitt, you need to put up or shut up. You can dish it out but can't take it. Release the taxes!
Maybe it is time for Romney to "put up or shut up". Nevermind, he stays shut up. He will not discuss anything including plans, his taxes, religion, foreign bank accounts, etc. The only thing he says is "Obama is bad".