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Before cheering supporters, she predicted she would have more combined votes than her rival when the primaries end Tuesday night, claimed victories in key swing states and said that no contender will command enough delegates to claim the nomination.
"In the final assessment I ask you to consider these questions. Which candidate best represents the will of the people who voted in this historic election?" she said in an appeal to some 200 uncommitted superdelegates who hold the balance of power in the fight for the nomination.
"Which candidate is best able to lead us to victory in November and which candidate is best able to lead our nation as our president in the face of unprecedented challenges at home and abroad?"
Obama and his aides projected confidence, and even in defeat, he gained 16 delegates in Puerto Rico, leaving him 48 short of the 2,118 needed to clinch the nomination.
Contrary to Clinton, they predicted he was on track to gain a delegate majority shortly after the primaries in South Dakota and Montana, and questioned her popular vote claim. Her assertion includes estimates for caucuses in Iowa, Nevada, Maine and Washington state, where no official candidate popular vote is available. It also includes the results from Florida, where no campaigning occurred, as well as Michigan, where Obama did not receive any votes because his name was not on the ballot.
Campaigning in Mitchell, S.D., the Illinois senator praised the former first lady in terms usually reserved for a vanquished rival.
"First of all, Senator Clinton is an outstanding public servant, she has worked tirelessly during this campaign ... and she is going to be a great asset when we go into November," he told his audience. "Whatever differences Senator Clinton and I may have, those differences pale in comparison to the other side."
Obama's confidence in the outcome of the historic battle between a woman and a black for the nomination reflected the results of Saturday's meeting of the Democratic Party's rules and bylaws committee. Before an audience that jeered and cheered by turns, the panel voted to seat disputed delegations from Michigan and Florida, but give each delegate only one-half vote rather than the full vote sought by the Clinton campaign.
While the decision narrowed the gap between Clinton and Obama, it also erased the former first lady's last, best chance to change the course of the campaign.
With 93 percent of the precincts reporting, the Puerto Rico vote count showed Clinton with 243,542 votes, or 68 percent, to Obama's 112,852, or 32 percent.
A telephone poll of likely Puerto Rican voters taken in the days leading up to the primary showed an electorate sympathetic to Clinton - heavily Hispanic, as well as lower income and more than 50 percent female. About one-half also described themselves as conservative.
Nearly three-quarters of all those interviewed said they had a favorable view of Clinton, compared to 53 percent for Obama. One-third said they didn't know enough about Obama to form an impression.
The survey was conducted Tuesday through Saturday for The Associated Press and the television networks by Princeton Survey Research Associates International. It included 1,587 likely voters with a candidate preference; sampling error was plus or minus 3.1 percentage points.
Obama had a total of 2,070 delegates in The Associated Press count, including at least 16 from Puerto Rico. He also gained the support of two superdelegates during the day.
Clinton has 1915.5, including at least 38 from Puerto Rico, with one yet to be allocated from the day's primary.
There are 31 delegates combined at stake in Montana and South Dakota on Tuesday, and Obama's high command sounded confident that enough superdelegates were poised to quickly climb on and deliver him the nomination.
There have been numerous statements by party leaders in recent days indicating they favor a quick end to the presidential race so the party can begin unifying for the fall race against John McCain, the Arizona senator who wrapped up the Republican nomination months ago.
And while Clinton's campaign said it reserved the right to challenge the decision concerning Michigan's delegates, Speaker Nancy Pelosi rushed out a statement Saturday night that congratulated the committee "for its good work."
The California Democrat has been neutral in the race, but also has been calling uncommitted lawmakers in recent days, urging them to issue their own endorsements soon after Tuesday.
Robert Gibbs, a senior aide, did not rule out the possibility that Obama will seat the Michigan and Florida delegations at full strength if he is the nominee.
"I think any nominee may make some decisions at some point regarding those delegations," he said on ABC's "This Week."
Clinton's campaign chairman, Terry McAuliffe, appearing on the same program, declined to say what Clinton would do. "We'll see where we are when we finish up Tuesday," he said. "Then superdelegates will begin to move."
He, as well as Clinton's communications director, Howard Wolfson, said the former first lady had won more votes that Obama in the course of the primary campaign - an argument she placed in a new television advertisement in South Dakota and Montana, and one she makes to undecided superdelegates.
Gibbs disputed that - and Clinton's claim includes estimates for caucuses in Iowa, Nevada, Maine and Washington state, where no official candidate popular vote is available. It also includes the results from Florida, where no campaigning occurred, as well as Michigan, where Obama did not receive any votes because his name was not on the ballot.
Clinton's campaign objected to the rules committee decision on Michigan's delegates, saying it had arbitrarily taken four delegates away from the former first lady and awarded them to Obama. As a result, officials said she may seek a decision on the issue by the convention credentials committee, which meets shortly before the convention opens in Denver.
Harold Ickes, a top adviser to Clinton, said on NBC's "Meet The Press" no decision had yet been made.
"I have not had a chance to talk with Senator Clinton at any length about it, and obviously this will be a big decision. But her rights are reserved," he said.
But one of her strongest supporters, Pennsylvania Gov. Ed Rendell, sounded uninterested in a further challenge.
"I don't think we're going to fight this at the convention, because even were we to win it, unless it's going to change enough delegates for Senator Clinton to win the nomination, then it would be a fight that would have no purpose," Rendell said on CBS' "Face the Nation."