All of McGarrys power and influence on screen came from the way Spencer played him. A tough, clever, powerful, yet human and likeable figure. One minute Leo could be in the war room reviewing the plans for a military strike against a rogue nation, the next he would be in his office loosing another discussion with his assistant, Margaret, all the time it was well delivered by Spencer. His best scenes were where he kept the other characters from bringing down the nation.
Leo McGarry: You saw Sam's friend?
Sam Seaborn: How did you know?
Leo McGarry: I had you tailed.
Josh Lyman: You had us tailed?
Leo McGarry: Yes.
Sam Seaborn: Why?
Leo McGarry: On the off chance that you're as stupid as you look.
Spencer died on Friday after suffering a heart attack. This is a real case of life imitating art as in the TV show his character suffered a heart attack and had to leave his job in the White House for most of the 6th season. Since then he had returned to prominence in the show as the Vice-Presidential candidate. His temporary reduced role in the show seriously diminished the show, his death diminishes the whole of television.