Signs have slowly pointed toward a Lowe exit. Robert's heart attack last season had viewers speculating his impending death. Last week's announcement that Robert would not run for re-election left the fate and purpose of the character in question. Lowe's addition to the cast after guest-starring in the show's first season boosted ratings, and even though Lowe has excelled at meaty storylines and scenes with Calista Flockhart, Matthew Rhys and Sally Field, Robert has always remained a peripheral character.
Source: LA Times