Covert operations continued under President John F. Kennedy and his successors. In 1961, the CIA attempted to depose Cuban president Fidel Castro through the Bay of Pigs Invasion, however the invasion was doomed to fail when President Kennedy withdrew overt U.S. air support at the last minute. During Operation Mongoose, the CIA aggressively pursued its efforts to overthrow Castro's regime by conducting various assassination attempts on Castro and facilitating U.S.-sponsored terrorist attacks in Cuba. American efforts to sabotage Cuba's national security played a significant role in the events leading up to the Cuban Missile Crisis, which saw the U.S. blockade the island during a confrontation with the Soviet Union. The CIA also considered assassinating Congolese leader Patrice Lumumba with poisoned toothpaste (although this plan was aborted). In 1961, the CIA supported the overthrow of Rafael Trujillo, dictator of the Dominican Republic. After a period of instability, U.S. troops invaded the Dominican Republic in Operation Power Pack (April 1965) to prevent a Communist takeover. Without collaborators, a U.S. invasion against an army united with the people would have been difficult and costly in lives; in an optimistic estimate, the Pentagon believed that at least two full U.S. divisions were required to overcome the extensive armament the Dominican Republic had acquired as protection against a Haitian invasion.