Not sure what kind of commitment Snarlin' Arlen got from Obama, but he did get a promise from Rendell and Casey that changing to Democrat party would grease his path with $, party and union backing, etc. Sestak is on his own, unable to receive endorsements, etc., but he may pull off an upset in the primary even with the deck stacked against him just because he isn't Specter.
Arlen ran last time and won easily as a Republican against a Democrat with no $, no party endorsement, etc. because he got Rendell and the union's backing. All he had to do was get Bush and the Republicans to save him from Toomey in the primary. This election, there was no Republican president to save him from Toomey, so he changed parties.
PA doesn't have two parties, just one Republicrat party, and Arlen is their "boy." If they can drag him past Sestak to the general election, he will likely be an easy winner in the fall because Toomey will get zilch from the Republicrats and will be on his own.
Ping to Post #18. ;-)