Shrugging off a consensus among political analysts, focus group participants and snap polls that Romney had the better debate performance, Obama told a campaign rally in Denver "the fellow on stage last night" at the presidential candidates' debate was not "the real Mitt Romney" and said "if you want to be president, you owe the American people the truth."
"The remarkable thing was that the centerpiece of his campaign, and of his economic strategy, he tried to pretend didn't exist last night," David Plouffe, a top Obama campaign official, told reporters Thursday during the daily press briefing.
Plouffe said the Obama campaign will adjust to "that dishonesty."
"It's hard to remember a time in American politics where you had someone who's a major nominee for the presidency, being that fundamentally dishonest toward parts of his campaign platform," he said.
Former New Hampshire Gov. John Sununu, a Romney surrogate, said in an appearance Thursday on MSNBC Obama was lazy.
"What people saw last night, I think, was a president that revealed his incompetence, how lazy and detached he is, how he has absolutely no idea how serious the economic problems of the country are, and how he has failed to even begin to address them," Sununu said.
During the debate, Romney said Obama champions big government, taxes and regulations with "trickle-down government.''
"What we're seeing right now is, in my view, a trickle-down government approach, which has government thinking it can do a better job than free people pursuing their dreams -- and it's not working," Romney said at the University of Denver in the first of three presidential debates this month.
Romney said the slow economy proves the Obama administration's policies have failed.
"The proof of that is 23 million people out of work," he said. "The proof of that is one out of six people in poverty. The proof of that is we've gone from 32 million to 47 million on food stamps. The proof of that is that 50 percent of college graduates this year can't find work."
Obama defended his handling of the economy.
"We've begun to fight our way back, but we all know that we've still got a lot of work to do, so the question here tonight is not where we've been but where we're going," he said.
He later said, "Are we going to double down on the top-down economic policies that helped to get us into this mess, or do we embrace a new economic patriotism that says, 'America does best when the middle class does best?'"
Obama faces re-election amid tepid economic growth and a national unemployment rate of more than 8 percent despite 30 consecutive months of growth in private-sector hiring.
The Labor Department is to release a jobs report Friday, one of two before the Nov. 6 election.
A proposal by Romney to cut tax rates for all income brackets prompted Obama to say the cut would deprive the government of $5 trillion in tax revenues, mostly from the wealthy.
Romney responded: "I'm not looking to cut massive taxes and to reduce the revenues going to the government. My No. 1 principle is, there'll be no tax cut that adds to the deficit."
Obama rejoined that Romney couldn't cut taxes and cut the deficit without shifting the burden to the middle class.
"For 18 months he's been running on this tax plan, and now, five weeks before the election, he's saying that his big, bold idea is 'nevermind,'" Obama said.
Romney avoided several Obama attempts to pin him down on which tax deductions he would eliminate in his tax-reform proposals.
This prompted Obama to say: "At some point, the American people have to ask themselves: If the reason Governor Romney is keeping all these plans secret, is it because they're going to be too good? Because middle-class families benefit too much? No."
Obama has proposed raising taxes on income of more than $250,000, combined with spending cuts, to help reduce the deficit.
An instant CNN poll indicated two-thirds of respondents said they believed Romney won the debate, with a quarter saying Obama had won.
The survey of 430 registered voters had an margin of error of 4.5 percentage points.