The Nationals announced a few minutes ago they've placed Ian Desmond, who is expecting the birth of his first child, on paternity leave. To replace Desmond, they've called up outfielder Roger Bernadina.
Bernadina, who missed out on the final outfield spot in spring training when the Nationals decided to keep Laynce Nix and option him to Triple-A Syracuse, had a .267 average with a homer and two RBIs in 13 games this year for the Chiefs. It remains to be seen where he's going to get at-bats, with Nix, Jerry Hairston and Brian Bixler all capable of playing the outfield, but since he's only going to be up for a couple days while Desmond is with his wife, he's mostly here to give the Nationals another bat off the bench.
He's already on the 40-man roster, so the Nationals had few other options that wouldn't have required them to make a 40-man move. The only other position players on the 40-man roster who aren't in the majors are Jesus Flores, Corey Brown, Chris Marrero and Bryce Harper. Flores was just sent back to Syracuse, Harper is obviously a ways from being ready and neither Brown nor Marrero has played in the majors.
In my mind, you could've made a case for Marrero, just to give the Nationals another right-handed bat off the bench and possibly spell Adam LaRoche for a game or two, but Bernadina is the safe choice since he's already got major league experience.