From TV Guide:
Episode Detail: West Wing The Wedding
Airings: NBC - Sunday, 11, 08:00 PM
As the White House prepares for Vic and Ellie's wedding, Bartlet has to contend with a potentially catastrophic foreign situation. Meanwhile, the Santos campaign has a major staff shake-up as Election Day approaches. Lou: Janeane Garofalo. Ellie: Nina Siemaszko. Santos: Jimmy Smits.
Credits: Martin Sheen, John Spencer, Allison Janney, Bradley Whitford, Janel Moloney, Stockard Channing, Joshua Malina, Jimmy Smits, Mary McCormack, Tim Matheson, Lily Tomlin (not listed in that order)