(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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GE also paid 100% of the taxes "they owed" which amounted to 0. No, Mitt is not telling us a lie, he is just concealing the fact that his "taxes owed" was zero.
Mitt has tons of money overseas.
It is so easy for Romney to disprove Reid's claim. Just show that you paid your taxes by disclosing your tax returns. If you do not, then you are presumed guilty by your denial.
This is all easily solved when Mitt releases those returns, then he can call Harry a liar and we will all know that Mitt takes care of business. Until then there is a very good chance that Harry is right and Mitt used loopholes and possibly even tax amnesty to avoid paying taxes. Harry;s right he does have the offshore account and he should come clean about his finances instead of thinking that Americans are too stupid to ask or to know about his taxes.
Romney should release his tax returns and case will be closed. I'm beginning to believe he has some thing to hide.
Just release your tax returns Willard.
If Romney has nothing to hide let him release his tax returns.
Show me your papers Romney.
Romney is bluffing like a typical bully. Come on Mittens, let's see them.. I'll show you mine!
What is Romney hiding? First it was he was not part of Bain after 1999- that was a lie.So why not show us exactly what he made during those years and from what sources?
Show us your taxes , or shut up !
All of you who want to see MIttens' 1040's for the past ten years please stand up.
Releasing publicly a decade or so's tax returns would be "putting up." Spin it all you want, Mittens, but you clearly have something you don't want the public (and your political opponents) to see.
Smoke and mirrors. Show your cards Reid.
Romney has this a little backwards. Reid's accused him of not paying taxes. Demanding his source doesn't really do anything but play the blame game. Instead, Romeny releasing his tax returns to show that he did pay taxes would disprove Reid and discredit the annonymous source.
Democrats are getting so desperate and arrogant. Remember, You didn't build that! You think you are smart, there are a lot of smart people out there.
Got tax returns?
Flip flop the etch-a-sketch. Magic, all Obama's fault.
Show us your 12 years of taxes, Mr. Romney if you wanted to show that Mr. Reid is wrong. What are you hiding?
Maybe it is time for Romney to put up or shut up.Release your taxes then we will see what you are hiding.
Did Mr. 1% pay the 1% tax rate he was legally required to pay? Legally required is a euphemism for 'I used every tax loophole known to mankind and then some', but I paid the $100.00 that I legally owed. How very generous of you Mitt to contribute a hundred bucks to the American infrastructure that allowed you to achieve your financial success. Guess you really didn't build that.
Mr. Romney it would be a great idea if you would take your own advice and put up or shut up! If you are indeed not hiding anything show us the tax returns. Otherwise, many, like myself, believe you are hiding a whole lot of incriminating information that would derail your so-called campaign in a heart beat.
Reid must protect his source as we wait for Romney to show the tax returns!
Mean Mugging Harry Reid is no joke . . . just look at the two face expressions. Romney (looking like a twit) and Reid (looking like he will boot kick a republican). Romney the wimp, says, "Put Up Or Shut up" I bet you $10,000.00 Harry Reid will lay Romney down . . . Good night Gracie!
Mitt!!! Thats what the american people have been saying . Show us your taxes. We have a right to know if you're a tax dodger or not. Put up or shut up.
U put up or shut up... Mittens! Stop your whining and show us what you have paid, didn't pay, and who was paying U!!!