They call Pennsylvania the Keystone State. Now it may hold the key to a Democratic comeback in the House.

After a Pennsylvania Supreme Court ruling that validated a redrawn election district map, Ryan Costello, a Republican from the 6th Congressional district outside Philadelphia, has decided not to run for re-election, The Washington Post reports. His announcement on Sunday shocked state Republicans, who saw the 41-year-old representative as an up-and-coming member of the GOP.

Because the new configuration of the district map could cause Republicans to lose two seats in the Philadelphia suburbs, the state could swing Democratic in the midterm elections. Moreover, Costello’s retirement follows 23 other Republicans who have decided to retire, leaving their seats up for grabs and opening the door to Democratic control of the House.