The one thing that is not talked about enough I think is how consistent the Nats have been all year. They've had 1 losing "streak" of 5 games. Unlike the Reds and the Braves that needed long winning streaks to stay in the hunt, the Nats have been consistently winning series all year long. They don't need an insane hot stretch to stay in contention and they've done a good job so far of avoiding prolonged slumps.
I think that kind of consistency over 2/3 of the season so far is the best indicator for sustainability.
