The Red Sox have already added three pitchers to their rotation in the past week, but that hasn't stopped them from discussing a trade with the Nationals for front-line starter Jordan Zimmermann. Per Ken Rosenthal:

One of the many ideas the Nats proposed was Zimmermann and [Ian] Desmond for right-hander Taijuan Walker and shortstop Brad Miller, sources said. ... The Nationals also had conversations about Zimmermann with the Red Sox and other clubs, again targeting premium young talent, according to sources. Zimmermann's $16.5 million salary, though, almost certainly would limit the return. Which returns us to the original question: What exactly is the Nats' plan?

Right off the bat, the Nationals seem to be starting off in Phillies territory, except that their demands come for a player who isn't even under contract for longer than a year. Granted, the demands of Walker/Miller are for a package that also includes a second high-quality rental in Ian Desmond, but the Nationals certainly aren't aiming low. Walker is one of the best pitching prospects in baseball, and at just 21 years old already has 53 good innings to his name in the majors. The Red Sox have the ability to match that sort of offer (not that the Mariners seem willing to make it in the first place), but it would involve turning to Betts or Bogaerts in the majors.

As the Nationals and Phillies seem to be finding out, however, the game has changed in how it views these premium prospects and the expensive contracts they're so often traded for. It's not to the point where a player is only as valuable as their contract is efficient, but the value of a market price free agent contract, which is what Zimmermann (and Desmond) will very likely be in a year's time, is not worth a player with Walker's potential to produce at a high levels for years to come at a low price.

As with Hamels, Zimmermann is certainly an incredibly talented player. In his first four full seasons in the majors, Zimmermann has produced a 3.00 ERA, and is one of the league's stingiest players when it comes to free passes, coming in at just 1.7 walks per nine innings. If he hasn't had any bad years since fully breaking into the league, 2014 still saw him take his game to another level, striking out a career high 182 batters while walking just 29, holding opponents to a 2.66 ERA, earning him fifth place in a fairly stacked NL Cy Young race

If the Red Sox are really determined to find an ace, then it's going to be hard for them to do much better than Zimmermann without venturing into Max Scherzer territory. But if they're not willing to shell out top talent for Cole Hamels on a four-year deal, it seems unlikely they'll be willing to go to those same lengths to acquire a pitcher they will then have to pay more money over more years if they want to keep him past 2015. And even less likely that they shell out, say, Xander Bogaerts in order to then pay both Zimmermann and Desmond. Yes, Desmond's defensive chops look awfully appealing when looking at the ground ball rotation the Red Sox will trot out in 2015, but it's hard to imagine the club seeking out a blockbuster of that magnitude given their focus on financial flexibility.

For now, add Zimmermann to the wishlist right under (or above, or next to) Cole Hamels. He's available, and the Red Sox would love to have him. But for now, the demands just aren't in line with reality.