Garfield left Rosecrans' staff to serve Garfield's term in Congress. On the way he praised Thomas' stubborn defense and created a meme that stuck with Thomas. Granger made the correct choice and threw his reserve into supporting Thomas rather attempting to rejoin Rosecrans. In the aftermath of Chickamauga Rosecrans picked a fight with the families of McCook and Crittendon.
Grant, Sherman and Sheridan achieved high command. None of them sought out Rosecrans as a staff assistant. The command of the US army in the Civil War can be characterized as a conspiracy for entertainment purposes. But to be serious, the people that knew Rosecrans got along just fine without him.
I suspect that Lincoln found a command for him before the 1864 election just to maintain some control over his behavior because he was still part of the army.
Decent general, idiot at politics. 4.5