Fidel Castro is the only real-life current head of state to be portrayed on The West Wing. All other on-screen presidents and prime ministers have been fictional characters, while only a handful of others (Queen Elizabeth II, Yasser Arafat) have been mentioned.
Kate Harper's top secret personnel file actually consists of partially redacted pages from J. Edgar Hoover's secret files.
One of the entomologists makes a reference to Abigail Adams and the War of 1812. However, it was Dolley Madison in the White House in 1812, not Abigail Adams.
John Spencer and Brian Dennehy previously appeared together in the 1990 Harrison Ford drama Presumed Innocent (1990), which also featured Bradley Whitford (Josh Lyman) and Jesse Bradford (Ryan Pierce, Season 5 Recurring).