Alexy was DFA’d by the Rangers in early December to make room on the 40 man roster for free agent Andrew Heaney. The Nationals just signed Dom Smith, and with a full 40 man roster, they had to drop someone to make room for him. Alexy was the odd man out.
Smith, you may recall, is a former New York Met first round pick who has been bandied about as someone maybe the Rangers should have interest in at various points over the last few years, but who was non-tendered a couple of months ago after failing to hit the last two seasons. The Nats will see if they can get him straightened out and, if they do, I guess we can start spitballing again about the Rangers trading for him.
Alexy, meanwhile, will presumably end up on the waiver wire. The Rangers could theoretically claim him, likely with an eye towards waiving him soon thereafter and trying to outright him, though that would require opening up a spot on the Rangers full 40 man roster, and I doubt they are interested in doing that.