One of the subplots concerns Sam's obsession over the "Legal Tender Modernization Act", which aims at eliminating the penny. The act does exist and was actually introduced in May 2001 by Arizona Congressman Jim Kolbe. The act also aims at withdrawing the Susan B. Anthony dollar from circulation, and prohibiting any redesign of the $1 bill.
The trivia item below may give away important plot points.
In the first season episode "Mr. Willis of Ohio", the President yells at his daughter Zoe about her being careless and what the dangers to her could be. His off the cuff description of her abduction (at a club in the bathroom, Secret Service agents being shot in the head) is very close to the events that would take place at the end of season four when Zoe is abducted from a bathroom in a club and one of the Secret Service agents is shot in the head.