says she will remain in the presidential race "until there's a nominee." The former first lady declined to say whether that meant through the roll call of the states at the Democratic National Convention this summer.
Clinton also disclosed that she had lent her campaign an additional $6.4 million in recent weeks, additional evidence that her once front-runner campaign was in deep trouble.
Meanwhile, pocketed the support of at least four Democratic convention superdelegates on Wednesday, building on the momentum from a convincing North Carolina primary victory.
Clinton showed no sign of surrender, but former Sen. George McGovern, the party's 1972 presidential candidate, urged her to reconsider.
Obama was at home in Chicago during the day as his aides spread word that he would soon begin campaigning in states likely to be pivotal in the fall campaign. Aides relayed word of the four endorsements, expected to be made public later in the day. Both disclosures were meant to signal fresh confidence that the nomination was quickly coming into his possession after a grueling marathon across 15 months and nearly all 50 states.
Obama's campaign on Wednesday weighed ways to bring the drawn-out Democratic nominating process to a close while mapping out a strategy that will involve campaigning in battleground states where primaries have already been held.
Obama's drive to nail down the party nod was buoyed by a double-digit win in North Carolina and a stronger-than-expected run in Indiana, where he almost overcame Clinton.
Obama was expected to compete for the six remaining Democratic contests but to also turn attention to general election states, aides said.
Likely Republican presidential nominee has "run free for some time now" because of Democratic preoccupation with the ongoing primary fight, said Obama strategist David Axelrod. "I don't think we're going to spend time solely in primary states," he said. "We have multiple tasks here."
The Illinois senator was enjoying a rare down day in his hometown before returning to Washington, D.C., late Wednesday
He was expected to travel later in the week to Oregon, where he appears to hold the advantage, and then head to the Appalachian coal states of West Virginia and Kentucky, where Clinton seems to have the edge.
Meanwhile, in an e-mail to supporters soliciting contributions, Obama called his North Carolina showing "a decisive victory."
As for Indiana, "we did much better than all the pundits predicted, despite Republicans changing parties to support Senator Clinton, believing she would be easier for Senator McCain to defeat," Obama wrote. "Now is the time for each one of us to step up and do what we can to close out this primary."
Obama was 184.5 delegates shy of the 2,025 needed to secure the Democratic nomination.
His campaign made broad suggestions that it was time for the 270 remaining unaligned superdelegates — who will determine the outcome of the race — to get off the fence, claiming the delegate math leaves little path for a Clinton victory.
NBC's national delegate count currently stands at 1,422 for Clinton and 1,588 for Obama. NBC’s estimated superdelegate count stands at 273 for Clinton and 256 for Obama.
[There are differences in how news organizations count delegates, how they award superdelegates, how they account for states that have held caucuses but have not yet chosen their delegates, and how they project the apportionment of delegates within congressional districts where the vote was close. The Associated Press and NBC News conduct separate delegate counts.]
"We think the Clinton camp has gotten away with a little bit of creating these alternative views of reality," said Obama campaign manager David Plouffe.
Clinton's loan more than doubled her personal investment in her bid for the Democratic nomination. She gave her campaign $5 million earlier this year.
A campaign aide said Clinton gave her campaign another $5 million on April 11, more than a week before the Pennsylvania primary. She then again dipped into her personal wealth for $1 million last week and $425,000 on Monday, one day before the North Carolina and Indiana primaries.
Clinton's campaign reported raising $10 million online after her Pennsylvania victory on April 22. Evidently, the money was not enough and her fundraising was unable to keep up with her expenses heading into Tuesday's contests.
Moreover, Obama has routinely outspent her in primary after primary and has shown little difficulty tapping his vast network of donors. He spent more than $7 million on advertising head of Tuesday's primaries in North Carolina and Indiana to her nearly $4 million.
According to the latest campaign finance reports filed with the Federal Election Commission, Obama began the month of April with $42 million in the bank for the primaries to Clinton's $9.3 million.
But Clinton had debts of $10.3 million at the start of the month, much of it money owed to her main polling, phone banking and advertising consultants.
And in endorsing Obama, McGovern said Wednesday it's virtually impossible for Clinton to win the nomination. McGovern said he had a call in to former President Clinton to tell him of the decision, adding that he remains close friends with the Clintons.
"I will hold them in affection and admiration all of my days," he said of the Clintons.
McGovern's announcement comes a day before Clinton was scheduled to travel to South Dakota to campaign. The state holds its primary June 3 with 15 pledged delegates at stake.
McGovern said he had no regrets about endorsing Hillary Clinton months ago, even before the Iowa caucuses.
"She has run a valiant campaign. And she will remain an influential voice in the American future," he said.
But Obama has won the nomination "by any practical test" and is very close to a majority of the pledged delegates, said McGovern, who is 85.
It's time to unite the Democratic Party, he said.
"Hillary, of course, will make the decision as to if and when she ends her campaign. But I hope that she reaches that decision soon so that we can concentrate on a unified party capable of winning the White House next November," he said.