What was Eisenhower's metaphor for the global communist threat, and how did it impact the development and sustainability of U.S. Cold War foreign policy?

President Dwight Eisenhower's metaphor for the Cold War was best described by him during a news conference on April 7, 1954:

"Finally, you have broader considerations tht might follow what you would call the 'falling domino' priniciple.  You have a row of dominoes set up, you knock over the first one, and what will happen to the last one is the certainty that it will go over very quickly.  So you could have a beginning of a disintegration that would have the most profound influences."

What became known as "the domino theory" played a major role in the U.S. approach to foreign policy in Southeast Asia, leading to the development of the Vietnam War, and to the U.S. approach to the status of the islands of Quemoy and Matsu lying between Taiwan (Formosa) and mainland China.  

France, emerging from its occupation by the German Army and anxious to resume what it saw as its proper place on the world stage, set about to attempt to reconstitute its imperial holdings in what was known as French Indochina, a vast region in Southeast Asia encompassing Vietnam, Laos and Cambodia.  The Vietnamese independence leader and communist Ho Chi Minh led a guerrilla insurgency that eventually drove the French out of the northern half of the country, an effort climaxed with the humiliating French defeat at Dien Bien Phu in 1954. 

The United States had supported French efforts in Indochina in exchange for French cooperation in estabishing the North Atlantic Alliance.  With the French defeat in northern Vietnam, U.S. political leaders in Congress and in the White House worried increasingly about the spread of Ho Chi Minh's influence and, by extension, that of the Soviet Union and Communist China, throughout Southeast Asia.  What became known formally as "the domino theory" grew out of these concerns about a sweeping communist takeover of Southeast Asia.  It was postulated, including quite vocally by a young U.S. senator named John Kennedy, that a communist victory in Vietnam would lead to the collapse of governments in Cambodia, Laos, Thailand, Indonesia, and the rest of the region to communism.  Once the Vietnamese domino was knocked over, the other dominoes would fall.

This, then, was the metaphor for which Eisenhower became known.  The growing U.S. commitment to the defense of South Vietnam grew out of that, and the rest is history.

How did Eisenhower's metaphor for the communist threat impact US Cold War policy?

President Eisenhower’s metaphor was the metaphor of dominoes.  Eisenhower likened the countries of the world to dominoes stood on end in a row.  One domino being tipped over (becoming communist) would knock the next over and so on until all the dominoes had fallen.

This idea helped to shape American foreign policy during the Cold War because it made it seem as if any threat from communism anywhere could be a danger to the US.  If Vietnam fell, for example, so would all the other countries of Asia.  Eventually, this would mean that the Philippines and Japan would fall and America would lack allies and bases in Asia. 

Thus, Eisenhower’s domino metaphor helped convince policy makers that communism had to be resisted even in places far from the United States.