The Nationals Lucas Giolito is now the number one prospect in all of baseball, and is nearly ready to make his Major League debut, but this article is not about why he should be called up it's about what should be done to the Nationals' rotation when he is called up. The obvious decision would be to send Tanner Roark back to the bullpen, same as occurred last season, when Doug Fister and Jordan Zimmermann where still in the rotation. However Roark has struggled with the back and forth between the two roles. So far in his career in his each of the times he had to switch in the first four starts back from the bullpen his ERA has been 4.63 whereas all the rest of the time it sits at a much better 2.59. Similarly in his first 8 games in the bullpen after starting his ERA was 3.12, but later it drops to 2.33. Roark seems similarly good at both roles, but the transitions are very difficult it seems to me that the nationals need to pick a role for him and keep it, so he can settle in and pitch well.
Instead of Roark it makes a lot more sense to put Gio Gonzalez in the bullpen. Of course it sounds strange to put a adequate starter that is paid $12 million in the bullpen, but based on his stats as a starter it appears that Gonzalez would thrive in relief. In his starts on average the first time through the opponents lineup his ERA was a phenomenal 1.67, but later on when going through the lineup the second, third, and fourth time his ERA is a well below average 5.02. Based on this evidence it seems clear that Gonzalez would do much better as a one or two inning reliever, in which case he would not have to go through the lineup more than once and would be a lights out reliever instead of a mediocre starter.