The Clinton campaign is also counting on a win in Pennsylvania. However, the rules in that state also make it very hard for anyone to get a large majority of the elected delegates. Hillary already has commitments for 10 of the superdelegates vs. 2 for Obama.
http://www.postgazette.com/pg/08041/856368-176.stm Excerpts of the article:
"They are in addition to the 158 delegates to be chosen based on the April 22 balloting. Of those 103 will be awarded based on the voting in congressional districts, while another 55 will be determined by the statewide vote. Thirty-five of those are at-large delegates and another 20 spots are reserved for party and elected officials who, in contrast to the superdelegates, will be pledged to vote for their candidate at least through the first ballot in Denver.
The Democrats' proportional rules make it difficult to accumulate big margins of delegates... Those rules help to explain why Pennsylvania can expect to be a player in the Democratic nomination fight, but, at the same time, they make it unlikely that the results in the state would be decisive.
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"The Obama campaign would seem to agree that Mrs. Clinton holds the upper hand in the state, according to a Bloomberg News report last week on an internal document prepared by the campaign and mistakenly included in a public email. The state-by-state spreadsheet projected a 52 percent to 47 percent win for Mrs. Clinton in Pennsylvania, one that would result in an 83-75 division of the state's pledged delegates. Projecting the overall delegate distribution, the spreadsheet sees a virtual tie among pledged delegates going into the convention, a result that suggests the controversial scenario whereby unallocated superdelegates would determine the party's nominee."