Reid Wilson at the National Journal, in "GOP Pushing Dems to Retire," outlines, as you might guess, a plan by Republicans to pressure some Democrats to retire. Here's an excerpt:
An informal list of 17 members the NRCC believes can be convinced to step down, privately called the "Dem Retirement Assault List," makes clear the party needs Dem incumbents to step aside if they have hopes of taking back the majority. The NRCC has taken pains to attack those lawmakers in recent weeks.
There is only one Pennsylvania congressional representative on the list: Tim Holden