From NBC's Andrea Mitchell
Two top Specter supporters tell NBC News that Arlen Specter cannot overcome Joe Sestak's lead in Allegheny County (Pittsburgh) to win this Pennsylvania Democratic primary.
The Democratic Party officials say that Specter's lead in Philadelphia will not be large enough, and they think that, by 11:00 pm ET, it will be over.
They are confident that the lead of the Democratic candidate in the special election to succeed the late John Murtha will hold up.
With more than half of precincts reporting, Sestak leads Specter, 53%-47%.
*** UPDATE *** The AP just called the race for Sestak.