"These six weeks are one of the most critical periods for the Democrats," says Joseph Aistrup, a political scientist at Kansas State University in Manhattan, Kan. "The candidates will be floating a lot of trial balloons to see what particular angles work."
The audience is only partly the voters who will award Pennsylvania's 158 delegates.
Perhaps more important, analysts say, are the nearly 800 elected officials and party leaders known as superdelegates who may well tip the race; the ordinary Americans whose poll responses journalists use to gauge shifts in political momentum; and the Democratic leaders who will decide whether and how to proceed with do-overs of the primaries in Michigan and Florida, which had been stripped of their delegates because they moved up their contests in violation of party rules.
Clinton won Michigan and Florida. But Obama didn't appear on the Michigan ballot, and to honor the party sanctions, neither campaigned in the two states.
Those primaries, if replayed in some form, would throw 366 delegates back into play. But it would also raise the threshold to win the nomination from 2,025 to 2,208. According to an Associated Press tally, Obama now has 1,598 delegates and Clinton 1,487, including pledged and superdelegates. Neither candidate is likely to pile up enough pledged delegates – those awarded through voting – in the 10 remaining contests to seal the nomination.