Janssen was one of the remaining big bullpen names on the free agent market, and the Nationals reportedly showing some interest in him back in November. That interest likely increased after Tyler Clippard, their former shutdown right-hander in the bullpen, was sent to Oakland for Yunel Escobar. As it stands, Janssen will set up for closer Drew Storen in 2015.
The 33-year-old Janssen is a product of UCLA and was drafted by the Blue Jays in the fourth round of the 2004 MLB Draft, beginning his career as a starting pitcher, before being converted to a reliever full-time in 2007. Last season, Janssen, despite solid numbers, had the worst year of his career since 2010. He went 3-3 with a 3.94 ERA in 50 games last year, pitching 45.2 innings and saving 25 games in 30 opportunities. Janssen missed 37 games last season with an injury.
Over his eight-year big league career, Janssen has posted a 29-24 record with a 3.52 ERA. He became the Blue Jays' closer in 2012. Since that time, he has saved 81 games and worked to a 4.68 strikeout-to-walk ratio and a 140 Adjusted ERA+ over 162 innings.
Janssen will be missed in the Blue Jays bullpen. The Blue Jays are still looking for backend relief help, and have shown "limited" interest in acquiring Jonathan Papelbon from the Phillies. The Blue Jays could also turn to the free agent market, as two pitchers with closer experience remain in Rafael Soriano and Francisco Rodriguez. The loss of Janssen may cause them to spend some money on another free agent.
For the Nationals, Janssen adds to a bullpen that had some struggles at the end of last season, especially when Soriano, then the Nationals closer, was removed form the position and was replaced by Drew Storen. As a group, the Nationals bullpen posted the fourth-highest Wins Above Replacement (FanGraphs) in the league. They hope that Janssen will help to add to that.
Side Note: I correctly predicted the terms and team of Janssen's deal yesterday in my blog post about the top remaining free agent relievers. Check it out here.