The president struggled to lay out a vision for a second term except to say that he would make sure that the deficit would be cut in a "balanced" way that would avoiding hurting working people. He said he had promised four years ago to "fight every single day on behalf of the American people, the middle class, and all those who were striving to get into the middle class. I've kept that promise and if you'll vote for me, then I promise I'll fight just as hard in a second term."
He said that Romney was reluctant to discuss details of his tax-cut plans that he said would cost $5 trillion, ridiculing the challenger's explanation that he would lower rates, but not the amount of revenue collected because he would cap deductions and exemptions.
"For 18 months he's been running on this tax cut. Now, five weeks before the election, he's saying his big, bold idea is, 'Never mind,' " Obama said.
Romney retorted: "Virtually everything he just said about my tax plan is inaccurate."
Obama and Romney shared the stage in Magniss Arena at the University of Denver for 90 minutes as equals, the president shorn of the trappings of his office and facing his challenger from a distance of about six feet.
Independent analysts and even some Obama partisans said Romney did better on the Denver stage.
"The president got schooled," said Daniel F. McElhatton, a Philadelphia-based Democratic consultant. "He didn't seem like he cared. He had the opportunity to close it, to seal the deal, and he didn't do it. . . . I don't understand why he let Romney control the debate."
For instance, McElhatton said, Obama should have been able to hit Romney harder on various shifts in the former Massachusetts governor's positions over the years. "He and his team did not prepare to do that."
Obama "seemed uncomfortable - not confident," said Lara M. Brown, a political scientist at Villanova University. "He also seemed frustrated with having to defend his record. I had that sense that . . . he didn't imagine he'd have so many facts coming at him. He seemed to want to talk theories and ideas, and share stories about people he believes his policies will help. Romney was more in command of the facts and was stronger in his delivery."
Bill Galston, a senior scholar at the Brookings Institution, said Romney did what he needed to do: have a strong enough performance to give himself some breathing room in the race.
"Romney presented himself as a reasonable man - neither an extremist nor an ideologue," said Galston, who served in the Clinton administration. "He calmly rebutted familiar attacks on his proposals. He was clear and forceful, tough but respectful. . . . He conveyed an impression of competence and experience as a potential manager of the economy."
But Romney "didn't answer any question," said Mayor Nutter, in Denver for the debate. "We still don't know what his tax plan is. The president gave a lot of detail and was specific in his responses."
Even as the two men met here, voters across the nation were already returning a verdict, with early voting under way in 35 states. The target: a small, elusive pool of undecided voters that could tip the balance in key states.
For Romney, the debate was probably his best chance in the last month of the campaign to reverse a tide that has been moving against him.
With less than five weeks remaining until the Nov. 6 election, Obama has pulled to a small but discernible lead in most opinion surveys nationally and in the swing states that will decide the election. At the same time, Romney has been dogged for a couple of weeks by the furor over a leaked video in which he dismissed 47 percent of Americans who pay no federal income taxes as "dependent on government" and "victims."
Obama did not mention that remark during the debate. But throughout the evening, Romney took care to try to undo some of the damage from those words, which had made him seem callous. He described the struggles of people he has met on the campaign trail and said, "The reason I am in the race today is there are people who are really hurting today."
The Denver debate was focused on domestic policy, with six 15-minute blocks devoted to the economy, health care, the proper role of government, and leadership. It was the first of three televised face-to-face encounters likely to dominate the campaign through Oct. 22.
Obama and Romney will also meet Oct. 16, in a town-hall-style debate on Long Island. Foreign policy is the subject of a third debate, in Boca Raton, Fla., on Oct. 22. Vice President Biden and Rep. Paul Ryan, Romney's running mate, are scheduled to debate next Thursday in Danville, Ky.
Presidential debates have produced moments that are considered pivotal: a haggard Richard M. Nixon next to the vigorous JFK in 1960; George H.W. Bush glancing at his watch during a town-hall debate in 1992; Ronald Reagan in 1984 answering a question about his advanced age by saying he would not make an issue of Walter Mondale's "youth and inexperience"; Al Gore sighing and rolling his eyes in 2000.
Yet political scientists who have sifted through the available polling evidence have found debates have rarely, if ever, shifted enough votes to decide a presidential election by themselves.
A Wall Street Journal/NBC poll released Tuesday suggested that 5 percent of the electorate nationally remained up for grabs, the audience both candidates were aiming to reach Wednesday.
A new survey of undecided voters in four Western states illustrated the influence the debates could have on those who remain persuadable at this late stage of what has been a polarizing election.
More than 7 in 10 undecided respondents in Colorado, Nevada, Arizona, and New Mexico said they would tune in to the debates, contrary to the image of undecided voters as uninterested. Just over 40 percent said the debates would have the single greatest effect on their decision.
Mike Melanson, a Democratic consultant who helped elect Colorado Gov. John Hickenlooper, said undecided voters are frustrated with partisanship, and are comfortable seeing both sides of issues - and want leaders who feel the same way. "They're looking for that authenticity of character," Melanson said.
There was a quick moment of laughter at the debate's outset, when Obama referred to first lady Michelle Obama as "sweetie" and noted it was their 20th anniversary.
Romney, smiling, even seemed to make the most of that moment. He offered his best wishes, and said to the first couple, "I'm sure this is the most romantic place you could imagine, here with me."
Contact Thomas Fitzgerald
at 215-854-2718, firstname.lastname@example.org, or follow @tomfitzgerald on Twitter. Read his blog, "The Big Tent," at www.philly.com/BigTent.