"We are at a defining moment in our history," he said. "Our nation is at war. Our planet is in peril. The dream that so many generations fought for is slipping away."
The Illinois lawmaker spoke to nearly 2,000 at an afternoon rally at St. Peter's College in Jersey City. He also attended a private fundraiser in New York, Clinton's adopted home state, on Wednesday night.
Obama started the event late, but said that was because he greeted the some 500 people outside who couldn't get into the small basketball arena at the Yanitelli Center.
Among those waiting outside was Ida Yongo, 45, a native of Kenya who lives in northern New Jersey.
"So many people are talking about change. I want to see what he has to say," she said.
Daphne Dixon, 40, of Jersey City, said she admired Obama's consistent message.
"He stands up for what he believes in. He's his own man," she said. "Hillary is just going to be a continuation of Bill Clinton."
Obama's campaign, riding high after he defeated Clinton and John Edwards in Thursday's Iowa caucuses, saw its momentum blunted somewhat in New Hampshire, where Clinton upset Obama on Tuesday, resurrecting her bid for the White House.
"We are in a position where we had some good results in Iowa, and we want to keep building on that momentum," said Mark Alexander, New Jersey state director of the Obama campaign, speaking Tuesday before the New Hampshire results were known. "We've been focusing on the early states, and we want to be really prepared in New Jersey and elsewhere to show everybody we can carry this through to the nomination."
New Jersey is one of 22 states holding primaries or caucuses on Feb. 5.
Obama has consistently run a distant second to Clinton in New Jersey polls. The most recent survey, taken in December by the Quinnipiac University Polling Institute, had Clinton at 51 percent, compared to 17 percent for Obama and 7 percent for Edwards.
Assemblyman Neil Cohen, a Union County Democrat and an early Obama supporter, said such polls became irrelevant after Obama won Iowa.
"Obama's been proving points steadily," said Cohen. "No one thought he could raise money, and he's now at $90 million, which is either close to her, tied with her or in the same ballpark. No one thought he could put together these grassroots organizations. These organizations are everywhere, and they've been working quietly behind the scenes since February."
Alexander said any result is possible in New Jersey.
"We don't think anybody should take any state or any voter for granted," said Alexander. "There is every reason to believe we can do well in New Jersey. This (rally) is to tell everybody we are going to run for the presidency of the United States and New Jersey is an important state for us."
The Clinton campaign did not immediately respond to an e-mail message for comment Tuesday.
Obama last campaigned in New Jersey in October, when he hosted a rally for about 600 people in Newark. He stressed his opposition to the war in Iraq and focus on health care and education during a 45-minute address.
He was also in the Garden State in May, speaking to labor union members in Trenton about the need for affordable health insurance for all Americans.
In October 2006, he campaigned on behalf of Sen. Robert Menendez, who was running for U.S. Senate against state Sen. Tom Kean Jr.
Obama has also tapped the Garden State for campaign cash.
He has raised $1.8 million here through September, the second highest total among Democratic candidates. Clinton has raised the most of any candidate of either party, $3.4 million, according to the Federal Election Commission Web site.
