What potential danger did the u. s. face as a result of the soviet missiles in cuba?

The United States faced the potential of nuclear war with the Soviet Union and the possible destruction of much of the United States itself.

The first U-2 spy plane aerial photographs taken in October 1962 revealed that the USSR was installing ballistic missiles that were capable of launching nuclear warheads at the United States.  A second U-2 reconnaissance mission showed that the types of missiles being assembled on island of Cuba were powerful enough to destroy much of US territory. 

It has been said that the Cuban Missile Crisis was the closest the Cold War ever came to exploding into a full-scale nuclear war.