Yet what does she sacrifice if she stays in too long? "For the long run, it is neither sexism nor insiderism to say that unless she sweeps in Pennsylvania and also in primaries in places such as Indiana and North Carolina, the decision to end the race by dropping out will fall upon Clinton," E.J. Dionne writes in his Washington Post column.
"But there is a more immediate question facing her: As long as she is in the race, how will Clinton choose to win? The Clinton campaign needs to examine not what this fight has done to Obama but what it is doing to her. For all Democrats, the worst thing that has happened since January is the tarnishing of the Clinton brand."
Her strategy of taking to the fight to the convention may not pay off -- and not just because it could turn off superdelegates. "Hillary Clinton will not have enough pledged votes on the 169-member Credentials Committee to deliver a majority decision in her favor, according to an analysis conducted for Politico," David Paul Kuhn writes.
"Her only hope of getting the key committee to vote out a 'majority report' supporting her position rests on her ability to persuade an as-yet-undetermined number of the 25 members appointed to the committee by party Chairman Howard Dean to cast votes for her position."
(Anyone expect Chairman Dean to come to Hillary Clinton's rescue, for the sake of prolonging the nomination fight?)
The New York Times' Katharine Q. Seelye and Julie Bosman provide a history lesson: "Convention fights often spell ruin for a party. The 1980 experience for Democrats -- as well as a fight in 1968, and one in 1976 for Republicans -- all suggest that a bruising primary carried through the summer can contribute to defeat in November."
Still, they write, "Many historians and analysts say that while protracted primaries can weaken a nominee, bigger factors are usually at play. Voters are often swayed by whether they feel the country is headed in the right direction. They take into account whether primary battles are personal or political. They want to see whether the winner and the loser can patch things up. And time can make a difference."
But here's one reason we won't be hearing much from Obama about how Clinton should get out of the race: "One of the reasons that we're ahead in this race is, unlike some other campaigns, we think every state is important. And we compete in every state," Obama tells the Allentown Morning Call's John L. Micek. "We don't cherry-pick. We don't say, 'Oh, that's a caucus. That's a primary. That's a state with no African-American population or a big African-American population.' My attitude is that every state deserves our efforts."
He's not cherry-picking Pennsylvania counties, either. Philadelphia Daily News columnist John Baer marvels at the fact that Obama's bus tour stopped in Lancaster County: "Are you kidding me? This, for national Democrats, is a dead zone," Baer writes. "Yeah, many mainstream Democratic leaders are against him and all the usual trends point to Clinton winning PA, possibly big. But, trust me, Obama's planning, organization and site selection suggest an effort not interested in usual trends -- or in writing anything off."