Rob Lowe opens up about why he left The West Wing at the height of the show's popularity. Lowe played Sam Seaborn, the deputy communications director to Richard Schiff's Toby Ziegler in Aaron Sorkin's West Wing. During his time at the White House, Seaborn wrote speeches for U.S. President Josiah Bartlet (Martin Sheen). The character leaves his position to run for Congress, with Lowe exiting the NBC hit. Though he'd return for the farewell season, there was a lot of speculation about why Lowe left in the first place.

https://screenrant.com/west-wing-show-sam-seaborn-exit-rob-lowe-response/