According to a recent MLBTR article (Look! I made a hyperlink!) the Nationals are aggressively shopping John Lannan. In a further update (here) it looks like they locked down Edwin Jackson. This definitely leaves them with a glut of starters, prospects, out of option pitchers, and so forth. According to the MLBTR piece, they're most likely looking for a position player in return.
Now, I know some of us around here harbor a deep and abiding love for one Mr. Callaspo, but I could see Lannan for Callaspo as a viable swap. The Nats have a need of a steady defender like him, who has some positional flexibility within the infield, especially given some of the talk surrounding their up-the-middle combo of Ian Desmond and Danny Espinosa. I live and work in the greater DC area, and have seen these two play. Speculation around these parts is that long term, Desmond may be over his head in the Bigs as an everyday shortstop, and that Espinosa and his niftier glovework would eventually slide over across the diamond. Acquiring Callaspo would give them the flexibility to do this by plugging him in at second.
On our side, Lanna provides a number of benefits. He's a fairly reliable left-handed starter who is young(ish), and while I don't claim to be a stat-head, I think his numbers would translate extremely well to our ballpark, the Anaheim marine layer, and our solid defense. He's also affordable, and under control for another year. Acquiring him would definitely fill out our rotation nicely with another solid pitcher who can eat some innings, and provide the Soshinator with a nice combination of lefties and righties in the starting 5. Furthermore, trading Callaspo, as valuable as he's been, would also free up some roster flexibility.
Have at it!