The Nats picked up Sean Burnett and Nyjer Morgan from the Pittsburgh Pirates last year for Lastings Millidge and Joel Hanrahan. I have no idea how the Pirates would consider this a fair trade (it's a joke), but none the less, the Nats certainly benefitied from the transaction.
T. Plush has been a stand out, both offensively and defensively. A marked improvement over Lastings Millidge in every aspect of the game. To his credit, Sean Burnett isn't the worst option. Certainly better on average than Hanrahan or the left handed equivalent from last year Ron Villone. However, his numbers aren't quite doing it this year.
Burnett has appeared in 15 games this season. In 8 of his first 12 appearances, the Nats ended up losing the game. In his most recent 3 appearances, Burnett failed to record an out in 2 of them, on the other appearance he recorded an out, but gave up a run and a walk. Burnett is supposed to be a situational lefty pitcher to come in and get out lefty batters and maybe one more. The problem is: he's not so good at you know... getting out the lefty batters...
It's hard to say the Nats couldn't see this coming though. Burnett has a 4.37 ERA this year. At the end of last year, it was 4.70. Hopefully he can figure it out, but the Nats may want to look for a lefty specialist out there somewhere if he can't.