The Nats didn't get a reliever (Miller went to the O's) and instead got Asdrubal Cabrera for Zach Walters. Great? Good? Mistake?
Let's go over the "Two Goals" evaluation of the trade.
Did the Nats win the trade? Did they get back equal or more in value?
The answer to this is probably not. Asdrubal is a 2 month rental. Zach Walters is under team control until 2020. You can argue the value of Walters (and we will) but it's doubtful that whatever Asdrubal does in August and September (and beyond?) will add up to more than what Zach gives the Indians
Will the Nats win now? Did the Nats make the team better for the immediate future?
The answer to this is yes. Asdrubal was an All-Star as recently as 2012 but had a off 2013 and has not recovered in 2014. It's very likely what he is now is his new normal. What exactly would that be? Combine 2013 and 2014 and you get a line of .244 / .301 / .395. He doesn't get on base and his power, which was what made him special, is fading. That's the line of an average player. Defensively he's never been great and was kind of bad last year, but you'd probably qualify him closer to average than bad. Average hitter, average fielder. Doesn't sound like much.
Then you look at what he's replacing in Danny Espinosa. We love Danny. He can field like the Dickens (little known fact, Charles Dickens was a top-notch second bagger). But Ol' "Refuses Surgery Joe" can't hit. He had put up a line of .221 / .287 / .354, which is worse accross the board, enough worse than Cabrera to end any arguement you might have.
Yes he has put up a .309 / .385 / .494 line versus left-handed pitching. But there are two things to note here. First, there is a lot more right-handed pitching than left-handed and if he's that good vs LHP you can imagine how bad he is vs RHP (don't imagine - hurts the brain - .186 / .245 / .296). Second, it's in 91 PAs. That's not even a month of PAs for full-time players. Could Danny be a good hitter vs LHP? I think so. He pretty much always has been. Is he this good? Probably not. That's probably small sample fluctuation. If Danny isn't this good versus LHP than his value tumbles even further and right now it's already at a point where he is not giving a team as much as Asdrubal should. To satisfy your split curiousity, Asdrubal, has for his career been very steady as a switch-hitter .737 OPS vs RHP, .753 vs LHP, and year by year basically shows the same consistency. What he gives you, he gives you every day versus everyone.
As for Zach Walters you've probably heard by now that guys that have Walters minor league profile (Lots of K's, not many BBs) tend not to succeed in the majors. (See: Moore, Tyler) It suggests a problem identifying the strike zone, not just a guys swinging from his heels. Now the one thing you can say about Zach is that he's moved quickly up through the minors. In 2010 he was in low A-ball. by 2012 he'd gotten some AAA time. He stalled there for a year (.253 avg with 134 Ks and only 20 BBs last year - despite 29 HRs that's an obvious recipe for major league disaster) but this year has put up better numbers all around. .300 average, 62Ks to 20BBs so far. It's improvement but don't feel too bad, because it's improvement from "Oh My God, Kid. Have you ever taken a walk?!? No WAY you'll succeed" to "I don't like your chances, Kid"
Best reasonable case for Zach? He spends a year or two figuring out major league pitching like he did in the minor leagues. Gives the Indians a few starting years including a couple .240 high 20 homer years in his late 20s before petering out.
Worst reasonable case for Zach? He can't hang with major league pitching at all, becomes a career minor leaguer who might give you one surprise good bench year in the majors (again See: Moore, Tyler)
My best guess? Bounces up and down for a few years, then maybe has one decent year of half-starting and a couple other borderline seasons where his value is mainly in the fact he's a 3B, SS, 2B type of bench player.
All in all the Nats didn't give up that much here. Certainly not someone you could rely on helping the Nats this year. So they are better off for 2014.
The Nats needed another bat in the lineup that wasn't flat-out terrible 60+% of the time, preferably with adequate defense. Asdrubal gives them that. This doesn't necessarily solve the "one injury away" issue the Nats were dealing with, but it certainly softens the blow in that case, staving off the dreaded "easy inning" scenario that that might have created.
The Nats are better today then they were yesterday, and they were good yesterday. Hard to complain.