It's just one Congressional district but Joe Sestak is doing very well in PA-12, which is a long distance from his home base in the Philadelphia suburbs. He leads Arlen Specter 44-35 there.
Democrats in the district give Specter pretty tepid reviews with 42% approving of his job performance in the Senate and 39% disapproving. Sestak is still relatively unknown with 37% of primary voters having no opinion about him but among the ones who do he gets good reviews with 40% seeing him favorably and 22% unfavorably.
As I wrote on Friday Sestak's potential victory on Tuesday is not an example of the left flexing its muscle. Among liberal voters in the district Sestak and Specter are actually tied at 44% each. Sestak's lead comes largely thanks to a 49-21 advantage among conservatives within the party who make up 26% of the primary vote in this district, almost equal to the 25% who identify as liberals. Sestak is also up 41-36 with moderates.
I have no idea how predictive, if at all, PA-12 is of winners in Democratic primaries but the numbers here would seem to bode well for Sestak.