Rep. Tim Holden (D-Pa.) will face a primary challenge following a redistricting process that made his congressional district considerably more Democratic.
Holden, a member of the fiscally conservative Blue Dog Democrats, voted against his party's health insurance reform law and against its bill to regulate carbon emissions for global warming.
He will face off against attorney Mark Cartwright, who in his announcement said he was from "the Democratic wing of the Democratic Party."
It is unclear how much money Cartwright will be able to raise or how much local support he has. He comes from a part of the state previously outside the Harrisburg-based district.
The congressman has shown himself to be a scrappy campaigner, winning an incumbent-on-incumbent match-up in his old Republican-leaning district in 2002 and surviving the 2010 Republican wave without too much of a challenge. But this is the first time he'll face a serious challenge from his left.