Mr. Obama held a rally at the Meadowlands in New Jersey, across the Hudson River from Mrs. Clinton’s home state of New York. And Mr. Romney, during his grueling 24-hour tour, spent much of the day trying to cast doubts on Mr. McCain’s conservatism.
The day showed how the dynamics of the race have shifted over the past month. Mrs. Clinton, who was long considered the Democratic favorite, found herself locked in a series of tight races with Mr. Obama.
On the Republican side, which only weeks ago seemed wide open, Mr. McCain sought to ride his recent victories and rising poll numbers to the nomination while Mr. Romney sought to win enough delegates to keep his campaign alive.
At his rally in Boston before an enthusiastic crowd, Mr. McCain proclaimed, “I believe we have every good shot at turning the state of Massachusetts around.” Asked about Mr. Romney’s displeased reaction to Mr. McCain’s foray into Massachusetts, the Arizona senator calmly replied: “I can’t account for any reaction. He’s certainly welcome to come to Arizona if he’d like.”
Afterward, Mr. McCain campaigned in Hamilton, N.J., and then went to New York City where he was endorsed by New York’s former governor, George E. Pataki, at an afternoon news conference at Grand Central Terminal. Mr. McCain was flanked by members of New York’s Republican establishment, including his onetime rival, former Mayor Rudolph W. Giuliani, Representative Peter King of Long Island and former Senator Al D’Amato.
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Mr. Giuliani, who endorsed Mr. McCain last week, told the crowd that the Arizona senator could win in November in parts of the country that are not normally fertile ground for Republicans, including New York. New Jersey and Connecticut. “We haven’t had a candidate like that since Ronald Reagan,” Mr. Giuliani said.
On Tuesday, Mr. McCain will also make a final trip to California for an appearance in San Diego and return to Arizona to watch the returns.
On the Democratic side, polls indicated that Mr. Obama, of Illinois, has narrowed Mrs. Clinton’s lead in such key states as California, Arizona and New Jersey. Nationally, the latest USA Today/Gallup poll showed a statistical dead heat, with Mrs. Clinton leading 45 percent to Mr. Obama’s 44 percent. Aides for both candidates have said they believe the race will continue beyond Tuesday’s results.
Mrs. Clinton began the day in New Haven with an appearance at Yale Child Study Center, where she had volunteered as a law student.
Mrs. Clinton was wearing the rigors of the campaign trail on her sleeve, speaking in a soft, hoarse voice, and frequently interrupting herself by coughing and sipping water. At one point, Mrs. Clinton raised her left hand to her cheek and brushed something away with her finger.
“I said I would not tear up,” she said. “Already, we’re not on that path.”
The emotional moment echoed a similar one in New Hampshire last month, when Mrs. Clinton’s eyes welled with tears as she talked about the tensions of running for president.
She reminisced about her law school days, when she arrived in New Haven “in an old beat-up car with a mattress roped to the top.”
Mrs. Clinton visited the center for a round-table discussion, but before delving into matters concerning health care, she talked about why she wanted to win the Democratic nomination.
“It does matter who our leaders are and what they do,” she said. “I’m now running for president because I think we can do better than we have.”
At a rally in the Meadowlands in East Rutherford, N.J., Mr. Obama repeated his message of change, saying voters are ready “to rise and create a new America.”
Joined at the podium by supporters, including Senator Edward M. Kennedy, Democrat of Massachusetts, Mr. Obama implored voters to see the race as a choice between yesterday and tomorrow.
“We have a real choice to make. It is a choice, not between black and white, not between genders and regions or religions, but a choice between the past and the future,” he said. “And if I’m running against John McCain, I want to be making the argument for the future, not for the past. I want to be going forwards, not backwards.”
Mr. Obama, who has grown accustomed to filling large venues across the country and did so throughout the weekend, spoke at the Izod Center in the Meadowlands before a crowd that the campaign estimated at 4,500 people. Only five sections of the arena were filled on Monday, in addition to the floor, while about two-thirds of the seats remained empty. Mr. Obama also visited Connecticut on Monday.
Mr. Romney is scheduled to cover the most miles throughout the day on Monday. The former Massachusetts governor began the day in Nashville, Tenn., where he appeared with Rick Santorum, a former Pennsylvania senator and conservative firebrand. Mr. Santorum hammered on Mr. Romney’s often repeated charge that Mr. McCain is insufficiently conservative to appeal to all Republicans, and he said Mr. Romney would lead a conservative charge to take the nomination.
“They want to show the bigwigs in Washington who is in charge of this party,” Mr. Santorum said.