: Following a heart attack during the summit, Leo steps down as Chief of Staff. In a surprising move, Bartlet appoints Press Secretary C.J. Cregg as his successor, forcing her to navigate a steep learning curve and the President's worsening multiple sclerosis.
Season 6 introduced several significant characters who reshaped the show's dynamic:
: Frustrated with the lack of viable Democratic candidates, Josh Lyman leaves the White House to run the dark-horse presidential campaign of Texas Congressman Matt Santos .