"The Obama campaign is looking for anything they can use to distract from the failure of the president to reignite our economy," Romney, the presumptive Republican nominee, said in an interview with the conservative National Review Online.
"I'm simply not enthusiastic about giving them hundreds or thousands of more pages to pick through, distort and lie about."
Earlier in the day, there was evidence the Romney campaign was heeding calls to fight back against Obama's damaging attacks on their candidate when surrogate John Sununu told reporters: "I wish this president would learn how to be an American."
Sununu, the former governor of New Hampshire, said Obama "has no idea how the American system functions."
"And we shouldn't be surprised about that, because he spent his early years in Hawaii smoking something, spent the next set of years in Indonesia, and when he came to the U.S. worked as a community organizer — which is a socialized structure — and then got into politics in Chicago."
Sununu later apologized for the remark, saying he "shouldn't have used those words."
But the increasingly nasty barbs reflect a presidential race that's getting more brutal by the day, in particular since the Obama campaign began accusing Romney of hiding something by refusing to release more tax returns while assailing him about the true length of his tenure at Bain Capital, the investment firm he founded and helmed.
Even fellow conservatives — including his one-time rival for the Republican nomination, Ron Paul —have urged Romney to release more than two years of returns.
"Politically, I think that would help him," Paul, the libertarian congressman who's retiring later this year, told Politico.com.
"In the scheme of things politically, you know, it looks like releasing tax returns is what the people want."
Indeed, a Public Policy Polling survey has found more than 60 per cent of independent voters — a crucial bloc of the U.S. electorate, hotly sought after by both campaigns — wants Romney to release more of his tax returns.
Another poll suggests Obama's onslaught is starting to hurt Romney in key battleground states, although the two men are still neck and neck in national surveys.
In a swing-state poll from Purple Strategies, nearly four in 10 surveyed said new information about Romney last week made them consider him less favourably than they had before.
Forty-two per cent of independents said Romney was "too out of touch" to be president, while in Colorado, Virginia and Ohio, his favourability numbers were slipping.
But Fergus Cullen, the former chairman of the New Hampshire Republican party, urged fellow Republicans to chill out.
"I don't know why so many Republicans are complaining right now," he said. "Romney is holding Obama under 50 per cent in several competitive states. He's raising more money than Obama, and no one thought that would happen. This is a good campaign; it's not a campaign that's in trouble."
During a campaign stop Tuesday in Pennsylvania, where voters have elected Democratic presidents for the past 24 years, Romney suggested Obama was opposed to the American dream.
"Do we believe in an America that is great because of government, or do we believe in an America that's great because of free people allowed to pursue their dream?" Romney asked a crowd of cheering supporters.
"President Obama attacks success and therefore under Obama we have less success. And I will change that."
Team Romney also seems intent on creating distracting buzz about his vice-presidential pick.
Word on Tuesday that two longtime Republican operatives have already been hired to work with the candidate's running mate fuelled speculation an announcement was imminent.
Announcing a VP pick this week could serve dual purposes: It would not only deflate Obama's attacks against Romney, but would allow Romney's running mate to campaign stateside when the former Masschusetts governor travels abroad later this month.
And yet Romney's reported short list of candidates doesn't include many political firecrackers to energize his campaign.
The list is apparently down to a final three: former Minnesota Gov. Tim Pawlenty, Ohio Sen. Rob Portman and Louisiana Gov. Bobby Jindal.
The most notable absence is Marco Rubio, the Cuban-American U.S. senator from Florida who was thought to be a near shoo-in just a few weeks ago. Romney campaign insiders say the two men lack a personal connection, and that the pro-immigration Rubio could cost him votes among the far right of the party.
Cullen says his money's on Portman — a relatively unknown legislator from one of the most crucial swing states in the union. Portman has met with Romney aides several times in recent weeks.
But Romney's not going to rush a VP announcement just because of bad press this week, Cullen said.
"The VP pick is something you'll live with hopefully for eight-and-a-half years, so you're not going to do it just to try to get away from a few days of bad headlines," Cullen said in an interview.
Portman is considered a safe bet: he's got lots of experience as a congressman, senator, budget director and cabinet member, in addition to a picture-perfect family life. He poses a low risk to the ticket, something particularly attractive to the Republican establishment after Arizona Sen. John McCain's ill-fated pick of Sarah Palin as running mate four years ago.
On Tuesday, McCain vehemently denied having chosen Palin over Romney in 2008 because of the contents of the millionaire's tax returns — a remark that quickly went viral and may end up doing more harm than good.
"We thought that Sarah Palin was the better candidate," McCain told Politico.com.
"Why did we not take Pawlenty, why did we not take any of the 10 other people? Why didn't I? Because we had a better candidate, the same way with all the others. ... Come on, 'why?' That's a stupid question."
Steve Schmidt, McCain's top campaign adviser four years ago, says it was Romney's vast wealth, not the contents of his tax returns, that gave him pause.
"Sen. McCain got caught flat-footed answering a question about how many houses he owned," Schmidt told the Huffington Post.
"In fact, they were Cindy McCain's properties but that distinction was lost in the political optics and we knew it would be a big liability that the presidential and the vice presidential candidates together owned more than a dozen homes. It was like something out of a 'Saturday Night Live' skit."Suggest a correction