“There’s nobody taking Hillary’s side but Hillary people,” said Donald Fowler of South Carolina, a former national party chairman and one of Clinton’s most prominent supporters, referring to her campaign’s suggestions that she might seek to challenge the way the party resolved the fight this weekend over seating the Michigan and Florida delegations. “It’s too bad. She deserves better than this.”

In a telephone interview Sunday from San Juan, Puerto Rico, Clinton still raised the possibility that she would challenge the party’s decision on seating those delegates. “Well, we are going to look at that and make a determination at some point,” she said. “But I haven’t made any decision at this time.”

Heading toward what is shaping up as something less than a triumphant moment of victory as the voting draws to a close, Obama spent Sunday in South Dakota for a last-minute schedule of campaigning. He was in the state, which will vote along with Montana on Tuesday to complete the primary season, trying to thwart a last-minute effort by Clinton to pull out a victory there and build her case that she would be the stronger candidate in the general election.

The dimensions of Clinton’s challenge were underlined as two more superdelegates signed on to Obama.

Clinton won by 2 to 1 in Puerto Rico, where she seemed to revel in a weekend of campaigning even as her surrogates fought in Washington to keep her campaign alive.

The victory—coming among Hispanic voters, who are a key constituency in the fall election—underscored a constant source of frustration among Clinton and her supporters: that her strong finish over the past months, with big victories among blue-collar voters, have shown no signs of pushing uncommitted superdelegates into her camp.

“Most Clinton supporters are filled with bewilderment that this is happening,” said Gov. Edward G. Rendell of Pennsylvania. “We are willing to go on, and we understand the inevitability of this, but we are filled with disappointment and amazement: Why haven’t these results caused the superdelegates to come around?”

Clinton, in the interview, in a new television advertisement and in her victory speech in San Juan, laid out why superdelegates should rally around her. She argued that by the time the final vote is counted, she will have more popular votes than Obama, an assertion that has been disputed.

“I think it will be most likely the case in a few days,” Clinton said from San Juan. “I will have won the most votes—more than anyone in the history of the primary process.”