The political pressure on Mitt Romney to release more of his personal income tax returns is causing some divisions inside the GOP presidential candidate’s camp, according to a Republican strategist close to the campaign.

Although some advisers are arguing privately that Romney needs to release additional filings to curb the political fallout, others are resisting that suggestion, reflecting the candidate’s longtime reluctance to publicly disclose information about his personal finances.

Kevin Madden, a senior adviser to Romney, would not discuss internal debate about strategy but said there is only one opinion that matters in the internal strategy debate.

“The final voice on this is the governor’s, and he’s made it very clear that the two years that he’s provided represent going above and beyond what’s required to be disclosed,” he said.

Asked about his taxes in a telephone interview Tuesday with National Review Online, Romney said: “The opposition research of the Obama campaign is looking for anything they can use to distract from the failure of the president to reignite our economy.”

He added: “And I’m simply not enthusiastic about giving them hundreds or thousands of more pages to pick through, distort and lie about.”

Late Tuesday, after the interview with Romney, the editors of the National Review wrote an editorial arguing that the only question for Romney is “whether he releases more returns now, or later — after playing more defense on the issue and sustaining more hits.”

The editorial adds to a growing chorus of Romney allies urging him to make the additional information public. In response to a reporter’s question at the State Capitol in Austin, Texas Gov. Rick Perry (R) also urged his former White House rival to be “as transparent as you can be,” although he appeared to stop short of calling on Romney to disclose more information.

The tax issue took center stage Tuesday in a campaign that has grown more acrimonious by the day, and Romney maintained that he would not release more than just the past two years of tax returns because he does not want to give the Obama campaign ammunition to attack him.

One reason for Romney’s reluctance is his belief that he will not be able to provide enough information to satisfy his critics.

“It’ll never be enough,” Madden said. “If you release 10, they’ll want 20. If you release 20, they’ll want 25, and whatever’s in there will be open to their distortions and their dishonest attacks.” The campaign has pointed to the fact that GOP nominee John McCain released only two years of returns during the 2008 campaign; Democrats have countered that McCain was the only one of the past seven White House challengers to release just two years of documents.

Many Republicans say Romney’s refusal to release the tax returns is beginning to cost him politically. “Perception is becoming Romney’s reality, and these issues have now risen above mere distractions,” said GOP consultant John Weaver, a senior adviser for McCain’s 2000 and 2008 bids. “The president has had the worst three months of any incumbent, due to the economy, since George H.W. Bush in 1992, and yet Romney has lost traction among key demographic groups in the vital swing states. He has got to get this behind him or he’s going to face summer definition a la [Bob] Dole and [John] Kerry.”

The Obama campaign began running a new tax-themed campaign ad in Pennsylvania on Tuesday and appears ready to continue pummeling Romney on the tax issue, with or without the release of his returns. The ad speculates that the former Massachusetts governor’s reluctance “makes you wonder if some years he paid any taxes at all.”

Among the Republicans jumping into the tax fray this week have been Rep. Ron Paul (Tex.), who told Politico on Tuesday that he thinks Romney should release more of his returns.

Fox News Channel’s Brit Hume weighed in on the matter Monday night, telling host Bill O’Reilly, “I don’t see any evidence that this is making a difference, but you know, anytime it’s disclosure versus non-disclosure, you always wonder whether it isn’t better to just put it out there.”

The two join Alabama Gov. Robert Bentley (R), former Mississippi governor Haley Barbour (R), and conservative commentators George F. Will and William Kristol in suggesting that the best move for Romney is to release the information.

The fight over Romney’s tax returns is part of a battle being waged by the candidates to control the turf on which the broader campaign is to play out.

For Obama, the goal is to focus on Romney’s private-sector background — a point on which the president hammered his GOP rival at a fundraiser Tuesday afternoon.

Romney’s “main calling card for wanting to be president is his private-sector experience, so we asked the voters to examine that experience,” Obama said at his first fundraiser of the day, at the Henry B. Gonzalez Convention Center in San Antonio, where he addressed a luncheon crowd of 1,200, including many Latino supporters.

At a rally in Pennsylvania, Romney seized on a remark Obama made during a campaign stop in Virginia last week to make his case that the president is ill-equipped to fix the country’s economy.

“He said this: ‘If you’ve got a business, you didn’t build that. Somebody else made that happen,’ ” Romney told the 700-member crowd at Horizontal Wireline, referring to Obama. “That somebody else is government, in his view.”

Romney added that he thinks the president wants Americans to be “ashamed of success” and that Obama is “changing the nature of America.”

“I find it extraordinary that a philosophy of that nature would be spoken by a president of the United States,” Romney said.

But just as the messaging battle has ramped up, so, too, have some of the envelope-pushing attacks from both sides.

Last week, the Obama campaign released a hard-hitting ad that appeared to question Romney’s patriotism and featured footage of the candidate singing.

On Tuesday, former New Hampshire governor John Sununu (R), a top Romney surrogate, suggested in a conference call with reporters that Obama doesn’t understand how the U.S. economy works.

“I wish this president would learn how to be an American,” Sununu said.

He later offered a clarification: “What I thought I said, but what I didn’t say, is the president has to learn the American formula for creating business.”

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David Nakamura in Texas, Nia-Malika Henderson in Pennsylvania and Chris Cillizza in Washington contributed to this report.