(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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Mitt talks tough on talk radio but when he has the chance to come clean, he is a coward. Go back to Salt Lake, Mitt. No way I am going to trust somebody who is in a cult. No way.
Please remember this. Romney did show 29 years worth of tax returns to John McCain in 2008. McCain then selected Palin for the V.P. nomination. He later stated that she was the better choice. That should speak volumes!
In the "Court of Public Opinion," the burden of proof is on Romney to prove he isn't a tax cheat.
It is time for Mitt to produce his returns that should, if he is being honest, shut up Reid.
There is moment to use “put up or shut up” this wrong moment
This is for Americans it will back fire
Romney could make all of these comments go away, just produce his tax returns for the last 10 years. He refuses, what is he hiding.
Mitt tells us he has enough courage to be the Commander in Chief – sending young men and women into battle – but he doesn't have the courage to show us his tax returns.
Obama will not even show us his College Application...Obama is dishonestly diverting weak minds from the economy to a non issue.
Where are your tax returns, Romney?
I'm sure if the IRS has a problem with what Romney has paid, Obama will pull a few strings to get the IRS on him. If Obama doesn't have a problem with Romney's tax payments, if the IRS doesn't have a problem ... why should we? Reid is a nasty politician.
All he has to do is release his tax returns to prove him wrong. Guilty until proven innocent – isn't that what the GOP told the President? So put up or shut up Romney.
My tax records are between the IRS and myself. if the IRS is happy with me then that is all anyone needs to know. There are a lot of people outthere that manipulate the tax laws on both sides, if you want to fix it change the complicated tax code.
I think it's about time for an all out AUDIT of mittens taxes.He might want to shut his trap.There's a reason he's not releasing his returns.
"Only little people pay taxes." Leona Helmsley
...or was it Mitten's wife's fancy horse?
Funny thing about reliable sources, you don't have to say who they are. Ball's in your court Romney, put up your taxes or shut up. If Reid is lying as you accuse, you can make all of this go away. But if you don't show your taxes I believe Reid is telling the truth.
oops! That should be Obama.. as in Obama 2012!!!
Put up your tax returns to counter Reid's comment, rather than use a grade 8 insult. Romney CLEARLY is hiding something.
"Put up or shut up." ??
It appears Mr. Romney missed the point... again. Can't wait to see a debate. Perhaps he'll try to send a stand-in.
Calling people dishonest for their acusations but not producing proof the acusations are false is dishonest in my opinion......
If Reid gets MItt Mad enough, Mitt will blurt out that he is a Great AMerican Arms Dealer and sells American weapons all over the World..Improving the sales of American gun makers....That is why he has Cayman Island bank Accounts and businesses in Bermuda...And Switz bank accounts...and why Mitt travelled to Israel and Poland...To sign new arms sales agreements...Ops...Maybe he should not have said that..
Just release them already, or does he have something to hide?
If Mitt Romney didn't pay his taxes, then he should probably be the subject of an IRS investigation and be fined accordingly. Haven't seen any indication that that is happeneing. Therefore, he paid his taxes as required by the law. The real problem is that senators like Reid lack the courage to legislate a NEW TAX CODE.
harry made all that cash from a land deal involving property he did not own for 3 years
Show all the tax returns and shut Mr Reid up himself.
What a bunch of bickering 5-year olds. Grow-up, politicos!