Barack Obama has gone on the offensive as he attempts to claw back following a televised presidential debate that his Republican rival Mitt Romney was widely perceived to have won.
The US president demanded "truth" from the "real Mitt Romney" on Thursday at a campaign rally in Denver, Colorado, as his aides promised a "hard look" at strategy after his listless performance in the previous night's face-off.
The candidates went head to head in a 90-minute jousting over jobs, taxes and health care.
"I met this very spirited fellow who claimed to be Mitt Romney," Obama said, accusing his Republican challenger of ditching unpopular positions on tax and education, adding: "if you want to be president, you owe the American people the truth".
At the Denver rally, Obama was fired up, passionate and engaged as he cheered up 12,000 supporters.
"It couldn't have been Mitt Romney because the real Mitt Romney has been running around the country for the last year, promising five trillion dollars in tax cuts for the wealthy," Obama said.
"So Governor Romney may dance around his positions. But if you want to be president, you owe the American people the truth.
"The fellow on stage last night said he didn't know anything about that. The real Mitt Romney said we don't need any more teachers in our schools.
"The fellow on stage last night - he loves teachers, can't get enough of them."
Romney, meanwhile, basked in the plaudits for his performance as he addressed a fund-raising event, saying Americans had seen two contrasting visions for the future on stage in Denver.
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He made a surprise appearance on Thursday at the Conservative Political Action Conference in Colorado, thrilling hundreds of attendees as he stepped on stage to join his sons who were scheduled guests.
"I know this is going to be a close-fought battle," he said.
"We need to win Colorado. You know what, if we do, we are going to win back the White House."
Obama seized on Romney's comment that he did not know anything about a break in the tax code for companies that outsource jobs overseas, adding that if it was true he needed a new accountant.
"He seems to be doing just fine with his current accountant," Obama said, in a jibe at the multi-millionaire former venture capitalist.
Obama also mocked Romney over his plan to to cut government subsidies for the PBS television channel that produces famed early learning show Sesame Street.
Al Jazeera's Patty Culhane, reporting from Denver, said: "Historically, presidential debates do not determine outcomes of elections, but in close races they do matter."
Obama's campaign team says he will make "adjustments," in the second presidential debate scheduled for October 16.
David Axelrod, Obama campaign strategist, said that the president will need to determine by the next debate how to counter what the campaign considers Romney's evasion on a series of issues.
He said Obama is "eager" for the next debate, adding that they will evaluate his performance and "make adjustments"
Boost for Romney
Romney has gained ground on the Obama after his strong debate performance, according to a new Reuters/Ipsos poll.
Romney is now viewed positively by 51 per cent of voters, the first time he has enjoyed a net positive in the presidential race, according to the poll released on Thursday.
Obama's favourability rating remained unchanged at 56 per cent.
Romney moved ahead of Obama on several core issues. Voters now see him as a better bet to boost the economy, spur job creation and manage the budget deficit, the poll found.
He narrowed Obama's advantage on taxes, Social Security and the Medicare health plan for retirees.
However, the latest NBC News/Wall Street Journal survey says 49 per cent of the people polled would vote for Obama, while 46 per cent said they would choose Romney.
The three-point difference is within the poll's margin of error, according to the pollsters.
The final two presidential debates are on October 16 and 22. Vice-President Joe Biden will debate Republican vice-presidential candidate Paul Ryan on October 11.
The US goes to the polls on November 6.