Nats should make trades only to improve for long term, and especially for next season. Do not trade prospects for any late-season rentals, not even if the team might be close to a wild card. That would be reaching for fool's gold. Senzel has looked good enough, to my surprise, while House is a year or two from the majors. As best I understand Senzel's contract, he is under Nats control through next season. If so, and if his improvement is real, offer him a two year extension. And keep Vargas.
Maybe flippage usually fails. The Nats got good prospects when they traded good players, like Trea and Soto, but not much when they traded middling players.
Of course, they should dump Gallo and Nunez, since both are a waste of space right now. Further, Gallo seems to have no trade value. If teams offer something good for Winker, take it. Too bad that Williams is hurt, and likely to be out until the deadline...or next year if his recovery lasts as long as Gray's has.
Promote Wood to the majors, and promote Crews to Rochester. Hold steady with Gray and be patient with Cavalli's rehab. Make Corbin an assistant assistant pitching coach as soon as Gray returns.