Conservative commentator Salena Zito on our four freshmen:

Emanuel struck gold in the Keystone State in 2006, impressively picking off four Republican incumbents...

The four won for a variety of reasons: Altmire because Hart refused to compete aggressively; Carney because of Sherwood’s personal behavior; Murphy and Sestak largely due to the political environment — voters moving away from Republicans.

So who’s vulnerable?

Not Patrick Murphy. He probably has done the most to establish himself as a quality incumbent who deserves re-election — certainly more so than the other three. From the work he has done pursuing a national veterans’ cemetery in Bucks County to securing $1.1 million for Delaware River flood prevention and repairs he gets the importance of paying attention to local issues. The only veteran of the Iraq war serving in Congress, he also co-authored legislation for a 21st Century GI Bill of Rights.

Probably not Sestak either. His seat in the southeast near Philadelphia has been held by a Democrat in the past and, based on the district’s voting performance, likely will be very hard for the GOP to win back.

Jason Altmire of McCandless is a maybe. A default winner the first time, his vulnerability comes into play if former Pittsburgh Steeler Lynn Swann runs a top-notch campaign against him.

Chris Carney’s seat in the northeast is probably most endangered. While much ado was made recently when U.S. Attorney Tom Marino dropped out of consideration, backbencher Dan Meuser is probably the better quality candidate anyway. He understands the issues, has charm and sports a sizeable personal checkbook. Marino was attractive, but this marks the second time in 10 years that he has floated his name only to pull out before his toe hit the water.

Then there are the pick-up opportunities high on the Democrats’ agenda; Republicans Tim Murphy of Upper St. Clair, Phil English of Erie, Jim Gerlach in Chester County and Charlie Dent in the Lehigh Valley.