"What she has to do is win Pennsylvania very big -- not by 10 points, but 15 to 20 -- so she can narrow that popular vote margin," said Shrum, a former adviser to Sen. John Kerry's 2004 presidential bid. "She has to defy expectations … win Indiana and show she's doing better, significantly better than Obama is, over John McCain.
"What worries me as a Democrat," he added, "is if we get to North Carolina and Obama wins ... and it's clear that he's going to win the pledged delegates, the super delegates are not going to overturn the pledged delegates. … We're not going to say, 'Let's see what electoral votes were assigned to the states that were won, because that proves you can carry them in the fall.'"
Shrum's comments go against an argument made earlier this week by Sen. Evan Bayh, D-Ind.
"Who carries the states with the most Electoral College votes is an important factor to consider because ultimately, that's how we choose the president of the United States," Bayh said in an interview on CNN.
How long the race goes on could well depend on Pennsylvania, a state that's been described as "Ohio on steroids," and is full of aging, white, working class voters, who have tended to favor Clinton.
The Clinton camp is arguing that electability comes from winning battleground states like Pennsylvania, where she currently holds a double-digit lead over Obama.
Obama is hoping an endorsement this week by the state's popular junior senator, Bob Casey, could help him win over some of those voters.
Today, Obama kicked off a six-day tour through the state and is currently outspending Clinton there, two to one.
"What Obama needs to show in Pennsylvania is momentum, a direction toward electability," said Donald Kettle, a professor of political science at the University of Pennsylvania, "the kind of thing that can convince the super delegates that he is the inevitable Democratic nominee."
"In some ways you could describe the Obama strategy in Pennsylvania as trying to win by not losing to badly," said ABC News political correspondent David Wright.
No End In Sight
On Friday, Sen. Patrick Leahy, D-Vt., an Obama supporter, became one of the first prominent superdelegates to call for Clinton to drop out.
"She has every right, but not a very good reason, but every right to remain a candidate as long as she wants to," Leahy said.
While campaigning through Indiana, Clinton took the news as just the latest twist in a long and drawn out fight for the nomination, which she had no intention of giving up.
"There are millions of reasons to continue this race -- people in Pennsylvania, Indiana and North Carolina, and all of the contests yet to come," Clinton told reporters Friday. "This is a very close race, and clearly I believe strongly that everyone should have their voices heard and their votes counted."
She heads to Pennsylvania early next week for three more weeks of campaigning before voters head to the polls there on April 22.
On Friday, Democratic National Chairman Howard Dean said he would like super delegates to announce who they are supporting by July 1.
Sen. Obama this week compared the fight for the Democratic nomination to "a good movie that lasted about half an hour too long."
When asked about it, Clinton joked, "I like long movies."