Updated 4:20 p.m. | Ryan Costello, chairman of the Chester County Board of Commissioners, announced Wednesday that he will seek the GOP nomination in Pennsylvania’s newly open 6th District.

Costello is the first Republican to announce a bid for the Keystone State seat, which is being vacated by GOP Rep. Jim Gerlach. The six-term congressman announced his retirement last week.

State Sen. John Rafferty is also eyeing a bid, Republican operatives say.

Businessman Mike Parrish, who filed federal paperwork to run for the seat before Gerlach’s announcement, is seeking the Democratic nomination for the seat. Democratic operatives describe him as a strong candidate.

Pennsylvania’s 6th District is rated a Lean Republican contest by Rothenberg Political Report/Roll Call. GOP presidential nominee Mitt Romney carried the district by a 2 point margin in 2012.

Updated 4:20 p.m. | Former state Rep. Sam Rohrer announced Wednesday afternoon that he will not seek the GOP nomination for the seat.

“I have prayerfully considered this decision, sought wise counsel from my family, pastors and my esteemed colleagues and have decided not to run for Congress,” Rohrer said in a news release.