Aaron Sorkin left The West Wing for financial reasons at the end of its fourth season. A great series often has trouble continuing on strong after losing its founding showrunner, but Sorkin went out of his way not to make things easy for John Wells, who had the uneviable job of replacing Mr. Walk-and-Talk himself.
Sorkin left the plot twisted as tightly as he could for Wells to unravel, going as far as to have the President's daughter kidnapped by the previous season's end. As a result, Wells had to spend a good chunk of season 5 getting himself out of the trouble that Sorkin had left for him. Though many viewers and critics agree that the final two seasons of the show did a fair job of regrouping the show, Wells' first season as shotcaller was a lost cause from the start.