The Nats aren't hitting. That's not as terrible as it sounds because as long as you are getting on base and hitting for power you can compensate for a low average. Now if you aren't hitting for any power...
Let's start with the good news. The Nats ARE getting on base ok. Not great, or even good, mind you. Unsurprisingly if you don't get a lot of hits, you don't end up with a lot of men on base. but they are doing ok because they have learned to take a walk. The Nats are tied for 5th in walks and their isoOBP is tied for 3rd (quick and dirty calc - basically they've had less PAs than other teams so their walks mean a little more.) Gone are the days of Nick Johnson taking a walk and then watching 8 guys go through 24 pitches before Nick came up again. Espinosa, Werth, and LaRoche can all work their way on base, and all are currently seeing 4+ pitches per at bat (ok fine, 3.99+). Zimmerman and Ramos aren't terrible at it either and Lombardozzi has this skill as well. So even though they aren't hitting at all (2nd lowest average at .225) they have a passable OBP (.301 - tied for 10th)
The problem is driving those guys in. The Nats are 3rd to last in homers. Sometimes that can be a product of the parks they've played in early on. So it's also important to note that they are third to last in doubles (and last in triples). Tied for dead last in the NL in XBH (50), last in the NL in isoSLG (.098) (fancy way of saying the precious few hits they are getting are mostly singles). 46 players in the NL have 3 or more homers. The Nats have one of these guys (Adam LaRoche - 4).
The problem is not just injuries, though sure injuries are a part of it. Even though I didn't have a lot of faith in Morse this year, surely he'd be slugging in some fashion and Zimmerman's being out doesn't help either (although he wasn't slugging much early on). But the whole LF situation has been a terrible drain on power (Bernie + Nady + DeRosa = 6 XBH or one more than Ankiel) and Danny Espinosa is facing a power outage that threatens his time in the majors. More than either of these though, it's a combination of everything. Werth and Ankiel (so far) have been ok (.150+ isoSLG). Zimm when healthy and Desmond passable(.115+) . Ramos, you can accept it (.089). The bench has been god awful - along with the OFs I talked about before, Lombo (1 XBH), Tracy (1), and Flores (0), are contributing no power. Sum the whole thing up and you have a team that no one fears is going to go deep on them.
Can things change? The hope is that Bryce and Moore will cover the pop until Zimmermann heals up and starts hitting and Morse comes back. That may be asking too much. Bryce hasn't found his power stroke since leaving Single A. Being somewhere on the high end of "passable" in his last 60 minor league games doesn't make me think he'll quickly become ok in the majors. Moore has a much better minor league power pedigree but also has K numbers that suggest he might get eaten alive up in the majors. Maybe he can hit .230-.240 and bang out some homers, or maybe he just won't hit at all.
The Nats may be fine in the 2nd half of the year. If Zimmerman is healthy, if Morse is healthy, if Bryce adjusts a little and Espy bounces back then the power can be... average. (You might balk at that but the Nats power was average last year with an incredible Morse and a very solid slugging Laynce Nix.) Average power with good OBP skills and some more luck getting basehits (they won't hit .225 for the year) and that may in fact be enough. From now until Morse and Zimm show they are healthy it will be rough in the run scoring arena, unless someone, hell someTWO go on a tear.