I think the Nats can lose game 3 and still win the series. Nats can get to Lohse in game 4.
That said, Nats probably need to win game 3. I think they are too young and inexperienced to win an elimination game. Especially with Detwiler on the mound. I'd feel better aobut their chances in an elimination game with Gio pitching.
On the above comments on Stammen, I wouldn't be too surprised if something is wrong with Burnett as well. He looked terrible and had several balls hit hard against him.