Excerpts from Books and Wikipedia
"Kennedy had castigated his Republican opponents for falling behind in this arena. Now he was under pressure to respond. He did so the following May, announcing a US program to put a man on the moon by 1970. . . . In short the political value of the mission was far more important than the scientific value. It also had the key advantage that a moon mission was never part of the Soviet space program. This was one race the United States was going to win." [Furtado: 1001 Days]