Episode Title: "Here Today" The title "Here Today" refers the old saying "Here Today, Gone Tomorrow" highlighting the staffing changes that took place in both Bartlet's White House and the Santos/McGarry Campaign.
Toby says to his attorney "Keep thinking, Counselor. That's what you're good at." This is reference to Butch Cassidy and the Sundance Kid, in which Sundance says the same line to Butch a couple of times.
When Josh Lyman interrupts Matt Santos and his wife to discuss staff changes, she is watching a Rob Zombie film, to which she reacts with a gasp and by covering her eyes. Santos asks Josh if he's a Rob Zombie fan, to which Josh responds, "I prefer his earlier, funnier movies." This is a sly reference to Woody Allen, many of whose fans were put off by his shift from the anarchic comedy of his earliest films to more introspective humor (and even drama) beginning with "Annie Hall." Allen himself parodied this in one of those films, "Stardust Memories," when space aliens tell Allen's character, "We enjoy your films. Particularly the early, funny ones."
The plot was likely inspired by the CIA leak investigation and the Valerie Plame affair.