FILE - In this Tuesday, Jan. 3, 2017, file photo, U.S. Rep. Ryan Costello, R-Pa., participates in a mock swearing-in ceremony on Capitol Hill in Washington. Costello announced on Sunday, March 25, 2018, that he would not be seeking re-election, ending weeks of speculation about his future and boosting Democratic hopes of winning his House seat. (AP Photo/Zach Gibson, File)

FILE - In this Tuesday, Jan. 3, 2017, file photo, U.S. Rep. Ryan Costello, R-Pa., participates in a mock swearing-in ceremony on Capitol Hill in Washington. Costello announced on Sunday, March 25, 2018, that he would not be seeking re-election, ending weeks of speculation about his future and boosting Democratic hopes of winning his House seat. (AP Photo/Zach Gibson, File)

WEST CHESTER, Pa. (AP) — A Republican Pennsylvania congressman has announced that he will not seek re-election, boosting Democratic hopes of winning his House seat.

U.S. Rep. Ryan Costello announced on Sunday that he would not be running, ending weeks of speculation about his future.

During an appearance on MSNBC, the second-term congressman called it “the most difficult decision” he’s ever had to make and said it was due to a number of factors including the state’s new congressional map.

Under the discarded map, Costello’s suburban Philadelphia district had a Republican majority that nevertheless helped Clinton beat Trump there by 2 percentage points in 2016. The redrawn district has slightly more Democrats and Clinton would have won it by 9 percentage points.

Costello was expected to face a tough election battle against Democrat Chrissy Houlahan.