But after losing momentum to Mr. Obama in February, she is now viewed by many party leaders as an obstacle to the fight ahead  even as she continues to argue that she is the best candidate, by dint of her experience, to carry the party’s flag into the “wartime election” fight against a Vietnam hero and national security pro like Mr. McCain.

Mrs. Clinton’s advisers say there is no party elder who has the stature or power to pressure her to bow out, aside from her husband, former President Bill Clinton. And he more than anyone wants her to keep running.

The nomination is not determined by the number of states won, but Mr. Obama’s inability to win major battleground states beyond Missouri, Minnesota, Wisconsin, and his home state, Illinois, is a concern of some Democrats  especially since Ohio and Florida have become must-wins in presidential elections.

Mrs. Clinton has been enjoying her first real burst of momentum lately, thanks to her new advertisements and speeches questioning Mr. Obama’s abilities in a crisis, raising the fact that he has not convened his Senate subcommittee to hold hearings on the Afghanistan war. A potentially embarrassing trial of a former Obama friend and contributor has begun. And major Clinton fund-raisers said that one big victory on Tuesday night would be enough to energize donors and keep $1 million or more flowing in daily.

“Each time people think we’re down, like after Iowa, or South Carolina, or the February primaries, Hillary has found ways to come back up,” said Jonathan Mantz, the national finance director of the Clinton campaign.

The results will also embolden her campaign’s efforts to persuade the Democratic Party to factor in the delegates from Florida and Michigan, her advisers say. The party counted out those states after they moved up their primaries; Mrs. Clinton stayed on the ballot in both and “won” them in January  despite having no real competition in Michigan and no real campaign in Florida. In a sign of her thinking, she shouted out to them in her Ohio victory speech Tuesday night.