I am sure most of you expected to see Trevor Williams' name here, and that would be a fine argument. In fact, you really would not need to argue at all. But I believe Williams can regain some value as a reliever/spot starter, as he excelled in that role with the Mets prior to signing with the Nationals. As a full time starter, he should not be back with the Nationals. But in theory, he still has some perceived value.
Now I am sure I will run into the group of fans that support the return of Dom Smith and cite his defense and clubhouse presence as reasons for a potential return, not to mention his cheap contract.
Well, first of all, it isn't your money so you don't have to worry about spending/not spending it. Also, the Nationals have more than $100 Million in spending space - they can afford a few extra million to upgrade the position.
The real reason to move on from Smith is that you NEED to upgrade offensively at first base. Look around the league - all the best teams have strong bats at first base. Dom Smith, on the other hand, currently has a .685 OPS and while he has hit 11 homeruns, nearly all of them have come in low leverage situations when the score is lopsided one way or another. While his defense has been strong, first base is not the position where you can sacrifice offense, especially that much offense, for defense.
Smith has not been the worst player on the Nationals this season, but his play has not proved enough to stick around. If the Nationals are serious about taking another step forward, they will make the necessary upgrade at the necessary power position.