"it shall be the policy of this nation to regard any nuclear missile launched from cuba against any nation in the western hemisphere as an attack on the united states, requiring a full retaliatory response upon the soviet union." which president found himself in a "showdown" with nikita khrushchev over the issue of soviet missile bases in cuba? a) john f. kennedy b) harry s. truman c) lyndon b. johnson d) dwight eisenhower