Marino will be first House member in current Congress to leave office early; 20 did so prior to the 2018 elections

U.S. Rep. Tom Marino (R-Pa.) announced that he will resign from office on January 23, 2019, to take a job in the private sector. It’s likely he won’t be alone in leaving his Congressional seat early—20 members of the 115th Congress (2017 and 2018) did so before their terms expired.
Seventeen U.S. House members left the 115th Congress early: 14 Republicans and three Democrats.
Democrats picked up three of the seats vacated by Republicans. All were in Pennsylvania, where Congressional districts were re-drawn by the state Supreme Court in early 2018: Pennsylvania’s 7th, 15th, and 18th Congressional districts.
Republicans did not flip any of the House districts vacated by a Democrat.
Three members of the U.S. Senate in the 115th Congress left office early: Thad Cochran (R-Miss.) Al Franken (D-Minn.), and Jeff Sessions (R-Ala.). Democrat Doug Jones won the seat that Sessions vacated. Republicans held the seat that Cochran vacated, and Democrats held the seat that Franken vacated.