WASHINGTON -- President Obama and Mitt Romney entered the final 48 hours of campaigning on Sunday with bravado tinged with urgent warnings to their supporters that the hard-fought race for the White House remained razor close.
The rivals started the day with rallies in the two competitive states where the presidential campaigns begin every four years and where the fates of their political futures could be decided this year at the last minute: Iowa and New Hampshire.
Joined by former President Bill Clinton in the shadow of the New Hampshire State House in Concord, Mr. Obama vowed to continue his efforts to improve a recovering economy and expressed the confidence of an incumbent that voters in the battleground states would give him the chance to try.
But he also betrayed the nervousness of a first-term president whose hopes for another four years -- and the opportunity to continue shaping his legacy -- hinges on a half-dozen states that could go either way on Tuesday.
"I am not ready to give up the fight, and I hope you aren't, either, New Hampshire," Mr. Obama said at a rally that attracted thousands of people, his voice already growing hoarse at the start of a long day of campaigning. "We have come too far to turn back now. We have come too far to let our hearts grow faint."
"We will win New Hampshire," he concluded. "We will win this election. We will finish what we started. We will renew those bonds that do not break."
Mr. Romney spoke moments earlier in Des Moines, also expressing the certainty of success and telling about 4,400 supporters that the clock had nearly run out on the president's time in office. He promised a new era of economic hope for families who are struggling.
"Instead of building bridges, he's made the divide between our parties wider," Mr. Romney said. "Let me tell you why it is he's fallen so far short of what he's promised: it's because he cared more about a liberal agenda than he did about repairing the economy."
Mr. Romney is racing from swing state to swing state with the intensity of a candidate who recognizes that he is trailing in the polls -- if only slightly -- behind Mr. Obama in many of the states he must win to accumulate the 270 electoral votes he needs to become president.
"We thank you; we ask you to stay with it. All the way, all the way to our victory on Tuesday night," Mr. Romney told the crowd, urging it to work hard in the last hours. "It's possible that you may have some friends or maybe even family members who haven't made up their mind yet who to vote for."
The two candidates have scheduled a flurry of rallies in the next two days to drum up the kind of enthusiasm that they hope will be evident at polling places on Tuesday.
Mr. Obama drew a crowd estimated at 14,000 people who gathered for an outdoor rally below the gleaming dome of New Hampshire's capitol. It was bright and chilly, recalling any number of days that he and other candidates had walked the streets of Concord to win the nation's first primary every four years.
Not far from where Mr. Obama spoke was a reminder of how New Hampshire almost dashed his dreams in 2008. On a line of granite stones in front of the State Library are chiseled the names of the winners of past primaries, including Hillary Rodham Clinton, whose victory in 2008 halted, for a time, Mr. Obama's surge after he had won the Iowa caucuses.
The president was to move on to Florida and Ohio on Sunday before making final stops in Wisconsin, Ohio and Iowa on Monday. Mr. Obama is expected to head home to Chicago on Tuesday to watch returns from his campaign headquarters.
Mr. Romney's schedule on Monday resembles the president's as he heads to the handful of states that could determine the results on Tuesday. Mr. Romney plans events in Florida, Virginia, Ohio and New Hampshire on Monday after visiting Ohio, Pennsylvania and Virginia on Sunday.
But Mr. Obama and Mr. Romney were only part of the battle on Sunday: their running mates, campaign advisers and a number of surrogates spread out in the swing states and made television appearances in an attempt to amplify the campaign messages.
Representative Paul D. Ryan, the Republican vice-presidential nominee, is spending Sunday in Ohio, Minnesota and Colorado. Vice President Joseph R. Biden Jr. began the day campaigning in Lakewood, Ohio, near Cleveland, and he was scheduled to travel to both Fremont and Lancaster, Ohio, before flying to Virginia, where he is scheduled to campaign in Sterling, a Washington suburb, and Richmond on Monday.
In Lakewood, Mr. Biden called for a return to a more bipartisan era, recalling Republican leaders including former Secretary of State Colin L. Powell; Senator Richard G. Lugar of Indiana, who lost the Republican primary this year to a Tea Party-endorsed candidate; and former Senators Chuck Hagel of Nebraska, Alan F. Simpson of Wyoming and Bob Dole of Kansas. "It used to work," Mr. Biden said. "We've got to get back to doing it again."
He suggested that Mr. Romney and Mr. Ryan would not be bipartisan leaders, saying, "I've never met two guys who are more negative about the country." Mr. Biden also strongly criticized the Republicans over their stance on women's issues, saying their views had not evolved for the 21st century.
Meanwhile, the top strategists for the presidential campaigns made their final appearances on the Sunday morning talk shows. Both sides described get-out-the-vote machinery that they said would provide the margin of victory.
"We think we're closing with strong momentum," David Plouffe, the president's senior adviser, said on the ABC News program "This Week."
"The president is having terrific events out there," he said. "So I'm confident, two days from now, the president will be re- elected. We have the support to win this election."
Mr. Plouffe dismissed the claims by Mr. Romney's team that he would will win the election, but acknowledged -- as did Mr. Obama during his remarks in New Hampshire -- that victory was dependent on the campaign's workers on the ground.
"We're throwing everything we can at this, but this really comes down to our amazing volunteers, our staff out in the field who have to make sure the people who support the president exercise their right to vote," Mr. Plouffe said. "So that's our biggest task right now, from a political standpoint, is to make sure that we get our vote out."
Ed Gillespie, a senior adviser to Mr. Romney, also appearing on "This Week," offered a very different assessment. Mr. Gillespie said that Mr. Obama was not doing as well as he did four years ago and would lose the White House to Mr. Romney.
"No 1, their ground game is not superior and, No. 2, I think those undecided voters are going to turn out, and they're going to break strongly against the president," Mr. Gillespie said. "When I look at the intensity numbers, when I look at being on the road for three days with Governor Romney and the crowds, when I look at the undecideds, I believe that Governor Romney will not only win on Tuesday, I believe he could win decisively."
The outcome could be affected by last-minute arguments over early and absentee voting, a subject over which the two parties have battled in court for months.
Ohio's top election official, Secretary of State Jon Husted, a Republican, will be back in court on Monday to defend a last-minute decision that critics say could invalidate thousands of provisional ballots.
Late last week, Mr. Husted issued a directive to county election officials saying that voters must correctly submit a form detailing the type of identification provided with their ballots. If the form is improperly filled in, Mr. Husted said, the ballot will not be validated. Voting-rights advocates quickly filed suit in federal court, saying that the directive was inconsistent with earlier court rulings and with Mr. Husted's previous instructions, which said that election officials -- not voters -- should fill out the form.
In Florida, a judge extended the early voting hours in Orange County after Democrats filed a lawsuit that cited a bomb threat that shut down an early voting location there for several hours on Saturday.
Democrats filed another suit to extend early voting across Florida. The balloting officially ended on Saturday. Republican lawmakers had shortened early voting to eight days this year, from 14 days four years ago. Democrats have complained that the action was taken to make it harder for supporters of Mr. Obama to cast their ballots.
In Miami-Dade County, election officials said they would keep their office open on Sunday to accept absentee ballots even though in-person early voting has ended.
Mark Landler contributed reporting from Concord, N.H., and Ashley Parker from Des Moines.
This article originally appeared in The New York Times.