Article published on the 2008-04-22 Latest update 2008-04-23 11:20 TU
"I'm not predicting a win," Obama told Pittsburgh radio station KDKA.
But he added that he thought the result would be closer than Clinton's campaign hopes. Her supporters expect to win a ten per cent lead because of white, working-class support in this industrial state which is going through hard economic times.
Analyst Andrew Hacker, of City College at New York University, points out that the state has many older voters with conservative voting habits.
Clinton needs to be well ahead to convince the party insiders, the so-called "super-delegates", who have enough votes at the Democratic convention to swing it her way, even if she doesn't have enough support among state delegates.
Obama has won 28 states to Clinton's 14 but she has seven of the eight big states and points out that no Democrat has ever lost the Pennsylvania primary and gone on to win the presidency.
Clinton has so far shrugged off pressure to stand down. But her campaign is now 10.3 million dollars in debt, while Obama's had 42 million dollars in its coffers at the beginning of April.
About eight million voters are expected to vote today. 200,000 have registered to vote in the run-up to this hard-fought primary.
2008-04-23 by Rosslyn Hyams