(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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romney what are you hiding????????????????????????????????
This is amazing that Romney is saying to Reid. Actually it applies to Romney himself. He should put up or shut up. By not releasing his tax returns he is admitting to not paying any income taxes. Let's go Rombo, let the nation see your tax returns.
So Mitt, lf Reid is so wrong, let' s see the tax returns. seems to me you are hiding somethIng!
if romney would put up harry would shut up
I believe Mitt, you are the one who needs to put up or shut up....what are you hiding?
I agree with Romney, put up or shut up. So Mitt, put up your tax returns or shut up your whining about people speculating why your breaking a long-standing tradition started by your father.
Easy fix, Romney! Release those ten years of tax returns!
Put up or shut up, isn't that the pot calling the kettle black!!! What a joke. Amazing how this guy skirts around the issue. The worse Presidential nominee that ever ran for the office.
Easy to put all this to rest Mitt –
Be transparent and level with us- the American people will forgive transgressions, but will also never forget nor forgive someone who tries to pull Nixon on them.
This is easy to settle! Let's see those returns!
Romney telling Reid to "put up or shut up"?
You can't make this stuff up.
Think Rom(o)ney got that backwards as he so often does - it's time for HIM to "put up or shut up!" Where, oh where, are those taxes returns? No tax returns = no confidence, no vote!
You first, Mittens!
How about Romney releases his tax returns when Obama releases his school records.
Harry Reid must be lazy to say Romney hasn't paid any taxes in 10 years. It took me 5 seconds to find his 2010 Federal tax return online and it shows he paid over $3 million in taxes. I hope the people of Nevada vote Reid out!
We want to see the last twelve years of your tax returns, Romney. It's that simple.
It has been reported by various outlets that Harry Reid has not addressed allegations of having engaged in pederasty, in effect making Harry Reid the Sandusky of the Senate.
The put up or shut up needs to be applied to Mr. Romney. Still no tax returns released...still waiting. What are you hiding, Mitt? So, Mr. Romney, this citizen says to you: "release your taxes like every other candidate, or shut up and go home." It is becoming clear that you are a liar and a tax cheat, a draft dodger, and your "retroactive" residency in Massachusetts does NOT cut it. You should never have even been governor of that state, since you didn't meet the residency requirements. You are a habitual liar and need to hush up and go away.
It is truly sad that legislators have immunity for slander while on the House or Senate floor.
So if its not true, release your tax returns to prove it. Like every other presidential candidate.
Shouldn't the answer actually be for Mitt to put up or shut up? Isn't he the one running for president and afraid to release his taxes even though his dad told him he should since it would be the proper thing to do?
Governor Romney should put up...his tax returns online. Then we'll see if we should shut up.
What are you hiding Romney???? Post your tax returns and end the untruthfulness of your opponents!!!!!
Innocent until proven guilty Harry.
Put up your tax returns.