Campaign Moods Shift as Contest Tightens Michael F. McElroy for The New York Times At a campaign event in Canton, Ohio, a supporter of President Obama listened to Vice President Joseph R. Biden Jr. BOCA RATON, Fla. - With a last aggressive debate performance behind him and 14 grueling days ahead, President Obama is now facing what he worked so hard to avoid: a neck-and-neck race with a challenger gaining ground when it matters most. Over the last month, through the debates and a gradual moderation of the conservative tone he struck during the Republican primaries, Mitt Romney undermined the Democrats" expensive summertime work of casting him as the candidate of and for the rich, emerging as a far more formidable opponent than Mr. Obama had ever expected. He continued down the path of moderation here on Monday night, agreeing with Mr. Obama almost as often as he disagreed. "For the first time in this race, I'd rather be us than them," said Senator Marco Rubio, Republican of Florida, crediting Mr. Romney's strength in the first debate as a critical shift in the campaign. They spent months building him up as one thing and one night he disproved it. The president, aware of deepening worry among Democrats about the prospect of losing the White House, was aggressive at the debate, belittling his rival's foreign policy experience in a bid to keep voters from seeing him as a credible commander in chief. But Democrats could only hope the candidates" final encounter here would level out a steady rise for Mr. Romney that has brought him to even with or leading the president in several national polls of likely voters. The race is suddenly so tight in the nine battleground states that each side is looking at a single Congressional district in Maine whose one electoral vote, in the event of an exceedingly tight outcome, could decide whether Mr. Romney or Mr. Obama is in the White House come Jan. 20. The growing sense of optimism inside the Romney campaign about his place in the race was visible in the newly relaxed faces of its senior advisers as they lounged poolside at their hotel in nearby Delray Beach before Monday's debate, ticking through states where they see new opportunities and rising poll numbers. Back in Boston, a senior aide marveled at how much the mood had changed from one month ago, gallows humor giving way to a realization that "we're in it." It remained a question whether Mr. Romney was gaining steam or riding a head of it from the strongest month of his campaign. Obama officials argued that the president's showing at the debate on Monday would remind wavering voters of his leadership in foreign affairs, a strong suit. They emphatically pointed to advantages he still holds in enough important swing states as their life line. "This race has automatically tightened as everybody in the Obama campaign predicted that it would, but he's ahead in the critical states," said Senator John Kerry of Massachusetts, Mr. Obama's debate sparring partner. But it is now unmistakable that Mr. Obama, who leaned forward in his chair at several points during the debate and glared at his rival, is focused on protecting some of his safest turf and Mr. Romney is seeing new opportunities to take it. Though polls have shown a mix of results, it is more often than not Mr. Romney who is on the upward trajectory, if not always overtaking Mr. Obama, then, at least, cutting into his leads among important constituencies. For instance a CBS News poll released Monday showed his edge among women was down to 5 percentage points from 12 a month ago. Another, from CBS News and Quinnipiac University, showed Mr. Obama's lead in Ohio among likely voters narrowing to 5 percentage points from 10 points last month. Mr. Obama will spend the next two weeks pitting the campaign machinery he built to push his voters to the polls against Mr. Romney's sense of momentum and new signs of hope in states that were tilting away from him only a month ago. Yet Mr. Romney still faces more of a challenge in the Electoral College and must win more of the battleground states than does Mr. Obama, who won all of them four years ago. Though they had been basking in their new sense of momentum, Mr. Romney's aides acknowledged that their hardest work could still lie ahead. They were hoping to break through Mr. Obama's firewall of supportive states while seeking new opportunities in places previously believed to be slipping out of reach, like New Hampshire and Nevada.