he had a 4.37 ERA in 24 games pitched, 15 of which were starts. Washington Nationals (2012-2017) Before the 2013 season, the Athletics traded Treinen to the Washington Nationals in a three-team deal, in which Washington also received A. J. Cole and Ian Krol, Oakland received John Jaso, and the Seattle Mariners received Michael Morse. With the Harrisburg Senators of the Class AA Eastern League, Treinen had a 3.64 ERA during the 2013 season. Major Leagues The Nationals invited Treinen to spring training in 2014, where he impressed Nationals' coaches. He began the season with the Syracuse Chiefs of the Class AAA International League, and was promoted to the major leagues on April 12. He earned his first career win on June 29, making a spot start against the Chicago Cubs and out-dueling Jeff Samardzija in a 7–2 win. During the 2014 Washington Nationals season, Treinen appeared both as a starting pitcher and out of the bullpen, with his fastball clocked as high as . Splitting the season between the Nationals and the Chiefs, Treinen had a 2.49 ERA in 15 major league games and a 3.35 ERA in 16 minor league games. For the 2015 season, Treinen started the year in the Nationals bullpen, with the off-season acquisition of Max Scherzer creating a crowded rotation picture. Manager Matt Williams, dealing with injuries to his veteran relievers, began inserting Treinen into high-leverage, late-game situations in early April, occasionally setting up for closer Drew Storen. He also reached with his sinker for the first time in his major league career during the first half of the season. Treinen remained with the Nationals for much of the year, posting a 3.86 ERA with a 2–5 record with 65 strikeouts for the season. He was optioned back to Syracuse on June 20 after struggling with command for the first half of the season. Upon being recalled the next month, Treinen told The Washington Post that being sent down "was probably the best thing that could have happened" in allowing him to work on his approach. However, even late into the season, Treinen was noted for struggling to retire left-handed batters, ultimately giving up the final run of the Nationals' season on a solo home run by left-hitting New York Mets outfielder Curtis Granderson in a 1–0 loss to the eventual World Series runners-up on October 4. In the Nationals' 2016 season, Treinen posted