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

While some advisers are arguing privately that the former Massachusetts governor should release additional filings to curb political fallout, others are resisting, 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 only one opinion matters.

"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 Tuesday in an interview 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, National Review editors 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 joins a growing chorus of Romney allies who have been urging him to make the additional information public. Texas Gov. Rick Perry on Tuesday 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 release more information.

The tax issue moved center stage Tuesday in a campaign that has grown more acrimonious by the day, and Romney maintained he would not release more than 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, he contends, is his belief that he will not be able to provide enough information to satisfy his critics.

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 only two years of documents.

The Democratic National Committee piled on with a Web video, trying to link Romney's tax returns to his being passed over as McCain's running mate in 2008.

The video says McCain had access to 23 years of Romney tax returns, but then named Alaska Gov. Sarah Palin as his running mate. "What does John McCain know that the American people don't?" the ad asks.

McCain on Tuesday called the inference "outrageous."

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 former senior adviser to 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 on Tuesday began running a new tax-themed campaign ad in Pennsylvania and appears ready to continue pummeling Romney on the tax issue, with or without the release. The ad speculates that Romney's reluctance "makes you wonder if some years he paid any taxes at all."

Among Republicans jumping into the fray this week have been Texas Rep. Ron Paul, who told Politico on Tuesday that 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 nondisclosure, you always wonder whether it isn't better to just put it out there."

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

Romney's best hope to quiet the attacks, unless he releases the returns, is to change the subject soon. His best chance probably comes at the Aug. 27-30 Republican convention, said Andrew Kohut, president of the Pew Research Center.

"He can present himself to the public and get a huge audience" and offer an unfiltered agenda, Kohut said. That forum was a big boost to other challengers who endured tough summers, notably Bill Clinton in 1992 and George H.W. Bush in 1988.

Information from McClatchy Newspapers is included

in this report.