Rainey was traded from the Reds to the Nationals on Wednesday in exchange for Tanner Roark.
Rainey made his major-league debut in 2018, though he struggled in his small sample, allowing 19 runs while posting a 7:12 K:BB in seven innings of relief. The 25-year-old fared much better in his first taste of Triple-A, notching a 2.65 ERA, 1.18 WHIP and 65:35 K:BB across 51 innings with Louisville. Rainey has the makings of a future high-leverage arm with a fastball that can touch triple digits, but he'll need to improve his control if he's to reach that ceiling.