Pennsylvania Rep. Ryan Costello reportedly plans to retire at the end of his term rather than seek re-election.
The two-term congressman reportedly plans to drop out before the May primary.
The news follows a state Supreme Court order that Pennsylvania's district map be redrawn due to gerrymandering that favored the GOP. Costello's a Republican, and his redrawn district now leans Democratic.
CNN reports that had the new lines been in place in 2016, Hillary Clinton would have won Costello's district by 10 percentage points.
Additional reporting by Newsy affiliate CNN.