DENVER (Reuters) - U.S. Republican Mitt Romney positioned himself on Tuesday for a high-stakes presidential debate, softening his stance on immigration while his campaign accused the White House of a "stunning admission" that it had failed on the economy.
Trailing in many polls, Romney is widely seen as needing to score a win at the televised debate in Denver on Wednesday night when the two men square off over domestic issues like the economy, immigration and healthcare.
Romney's campaign jumped on Vice President Joe Biden for comments the Republicans said were an acknowledgment that Obama's policies have been bad for the economy.
Accusing Romney of planning to raise taxes, Biden told a crowd in Charlotte, North Carolina:
"This is deadly earnest. How they can justify ... raising taxes on the middle class that has been buried the last four years?"
Obama's camp said Biden, known for making gaffes and speaking out of turn, was referring to the economic plight caused by former President George W. Bush's policies. But the Romney campaign made the most of the remark.
"Vice President Biden, just today, said that the middle class, over the last four years, has been 'buried.' We agree," Romney's running mate, Paul Ryan, told supporters at a campaign event in Iowa.
The Biden comment gave Republicans hope ahead of Wednesday's showdown in Denver, the first of three presidential debates that might define the November 6 election.
In the latest effort to show a gentler side after a damaging video appeared last month, Romney tweaked his immigration policy.
He told The Denver Post that he would not overturn an order by Obama in June that allows hundreds of thousands of illegal immigrants brought to the United States as children to stay in the country.
The former Massachusetts governor is struggling to score points with independent voters on immigration after suggesting in the Republican primaries that some 12 million undocumented workers should "self-deport" from the United States.
"The people who have received the special visa that the president has put in place, which is a two-year visa, should expect that the visa would continue to be valid. I'm not going to take something that they've purchased," Romney said.
Previously, Romney had not said whether he would reverse Obama's order, instead promising to put in place an immigration reform of his own that would make that kind of action unnecessary.
His softer stance on immigration appeared aimed at courting the Hispanic vote, which will likely be key in the swing state of Colorado. Nationally, Obama leads Romney among Hispanic voters by as much as 40 percentage points.
It is part of a bid by Romney's campaign to present a more empathetic face to voters after the former businessman was seen on a secretly recorded video deriding 47 percent of the electorate as dependent on federal aid.
A Reuters/Ipsos poll on Tuesday showed Obama's lead over the Republican narrowing to five points, at 46-41 percent. Obama was ahead by seven points last week and five points on Monday in the online survey.
Last week, Romney told voters in battleground state Ohio that his "heart aches" for the jobless and he has been bolder in defending his 2006 healthcare reform in Massachusetts as evidence that he cares for ordinary people.
Often accused of being out of touch with voters, Romney took a break from preparation for Wednesday's debate with Obama by visiting Mexican fast food chain Chipotle in Denver, where he ordered a "burrito bowl" of pork, rice, black beans, guacamole and a spicy sauce.
Obama goes into the debates appearing to have the momentum in the campaign despite high unemployment and criticism of his Middle East policy after last month's killing of the U.S. ambassador to Libya.
"The Romney campaign still seems to be trying to find a Plan B for going after the incumbent," said Dante Scala, a political science professor at the University of New Hampshire.
Obama's campaign accused the Republican of confusing voters in The Denver Post interview about whether he supports allowing the children of illegal immigrants to stay in the United States.
"There are a lot of questions that were raised about that interview. Again, it's not showing a huge amount of courage to give a confusing answer on an issue that's been around for more than 100 days," spokeswoman Jen Psaki said in Nevada.
Romney's comments may risk alienating conservative voters who applauded his earlier stand against illegal immigration.
"Problem is, the real conservative base will reel him back in. Talk radio will be on him by (Tuesday) afternoon," said Larry Berman, a professor of political science at Georgia State University.
Despite Romney's new course on immigration, Ryan has taken a harder tone. The Wisconsin congressman has vowed that Romney would overturn the kind of White House order that Obama used in offering work permits to the children of illegal immigrants.
"Here's the great thing about a Mitt Romney presidency. For an executive order that came from the last president, the new president can undo it," Ryan told voters in Lima, Ohio, on September 24. "We're planning that."
Speaking in Iowa on Tuesday, Ryan was quizzed by a voter about a Fox News interview last weekend in which he said he could not quickly explain to the interviewer which tax loopholes he and Romney would scrap to allow them to cut tax rates.
"Why aren't you more specific? I heard you, was it Sunday when you were on Fox? And you didn't answer his question about what are your plans," the woman asked.
Ryan said: "When you get into a math conversation, it can take a little while. ... There is plenty of fiscal room to keep these important preferences for middle-class taxpayers, you know, like charitable donations or buying a home or healthcare."
Additional reporting by Samuel P. Jacobs and Patricia Zengele in Washington and Jeff Mason in Nevada; Editing by Alistair Bell