Containment
He won wide support from both parties as well as experts in foreign policy inside and outside the government. It was strongly opposed by the left, notably by former Vice President Henry A. Wallace, who ran against Truman in the 1948 presidential campaign.
Truman, under the guidance of Acheson, followed up his speech with a series of measures to contain Soviet influence in Europe, including the Marshall Plan, or European Recovery Program, and NATO, a 1949 military alliance between the U.S. and Western European nations. Because containment required detailed information about communist moves, the government relied increasingly on the Central Intelligence Agency (CIA). Established by the National Security Act of 1947, the CIA conducted espionage in foreign lands, some of it visible, more of it secret. Truman approved a classified statement of containment policy called NSC 20/4 in November 1948, the first comprehensive statement of security policy ever created by the United States. The Soviet Union's first nuclear test in 1949 prompted the National Security Council to formulate a revised security doctrine. Completed in April 1950, it became known as NSC 68.  It concluded that a massive military buildup was necessary to deal with the Soviet threat. According to the report, drafted by Paul Nitze and others:

In the words of the Federalist (No. 28) "The means to be employed must be proportioned to the extent of the mischief." The mischief may be a global war or it may be a Soviet campaign for limited objectives. In either case, we should take no avoidable initiative which would cause it to become a war of annihilation, and if we have the forces to defeat a Soviet drive for limited objectives it may well be to our interest not to let it become a global war.

Alternative strategies: There were three alternative policies to containment under discussion in the late 1940s. The first was a return to isolationism, minimizing American involvement with the rest of the world, a policy that was supported by conservative Republicans, especially from the Midwest, including former President Herbert Hoover and Senator Robert A. Taft. However, many other Republicans, led by Senator Arthur H. Vandenberg, said that policy had helped cause World War II and so was too dangerous to revive.
The second policy was a continuation of the détente policies that aimed at friendly relationships with the Soviet Union, especially trade. Roosevelt had been the champion of détente, but he was dead, and most of his inner circle had left the government by 1946. The chief proponent of détente was Henry Wallace, a former vice president and the Secretary of Commerce under Truman. Wallace's position was supported by far-left elements of the CIO, but they were purged in 1947 and 1948. Wallace ran against Truman on the Progressive Party ticket in 1948, but his campaign was increasingly dominated by Communists, which helped to discredit détente.
The third policy was rollback, an aggressive effort to undercut or destroy the Soviet Union itself. Military rollback against the Soviet Union was proposed by James Burnham and other conservative strategists in the late 1940s. After 1954, Burnham and like-minded strategists became editors and regular contributors to William F. Buckley Jr.'s National Review magazine.
Truman himself adopted a rollback strategy in the Korean War after the success of the Inchon landings in September 1950, only to reverse himself after the Chinese counterattack two months later and revert to containment. General Douglas MacArthur called on Congress to continue the rollback policy, but Truman fired him for insubordination.
Under President Dwight D. Eisenhower, a rollback strategy was considered against communism in Eastern Europe from 1953 to 1956. Eisenhower agreed to a propaganda campaign to roll back the influence of communism psychologically, but he refused to intervene in the 1956 Hungarian Revolution, mainly for fear that it would cause World War III. Since late 1949, when the Soviets had successfully tested an atomic bomb, they had been known to possess nuclear weapons.

Korea: The U.S. followed containment when it first entered the Korean War to defend South Korea from a communist invasion by North Korea. Initially, this directed the action of the U.S. to only push back North Korea across the 38th Parallel and restore South Korea's sovereignty, thereby allowing North Korea's survival as a state. However, the success of the Inchon landing inspired the U.S. and the United Nations to adopt a rollback strategy instead and to overthrow communist North Korea, thus allowing nationwide elections under UN auspices. General Douglas MacArthur then advanced across the 38th Parallel into North Korea. The Chinese, fearful of a possible U.S. presence on their border or even an invasion by them, then sent in a large army and defeated the UN forces, pushing them back below the 38th parallel. Truman publicly hinted that he might use his "ace in the hole" of the atomic bomb, but Mao was unmoved. The episode was used to support the wisdom of the containment doctrine as opposed to rollback. The Communists were later pushed back to roughly around the original border, with minimal changes. Truman criticized MacArthur's focus on absolute victory and adopted a "limited war" policy. His focus shifted to negotiating a settlement, which was finally reached in 1953. For his part, MacArthur denounced Truman's "no-win policy."

Dulles: Many Republicans, including John Foster Dulles, were concerned that Truman had been too timid. In 1952, Dulles called for rollback and the eventual liberation of Eastern Europe. Dulles was named secretary of state by incoming President Eisenhower, but Eisenhower's decision not to intervene during the 1956 Hungarian Revolution, which was put down by the Soviet Army, made containment a bipartisan doctrine. Eisenhower relied on clandestine CIA actions to undermine hostile governments and used economic and military foreign aid to strengthen governments supporting the American position in the Cold War.

Cuba: In the Cuban Missile Crisis of 1962, the top officials in Washington debated using rollback to get rid of Soviet nuclear missiles, which were threatening the United States. There was fear of a nuclear war until a deal was reached in which the Soviets would publicly remove their nuclear weapons, the United States would secretly remove its missiles from Turkey and to avoid invading Cuba. The policy of containing Cuba was put into effect by President John F. Kennedy and continued until 2015.

Vietnam: Senator Barry Goldwater, the Republican candidate for president in 1964, challenged containment and asked, "Why not victory?" President Lyndon Johnson, the Democratic nominee, answered that rollback risked nuclear war. Johnson explained containment doctrine by quoting the Bible: "Hitherto shalt thou come, but not further." Goldwater lost to Johnson in the 1964 election by a wide margin. Johnson adhered closely to containment during the Vietnam War. Rejecting proposals by General William Westmoreland for U.S. ground forces to advance into Laos and cut communist supply lines, Johnson gathered a group of elder statesmen called The Wise Men. The group included Kennan, Acheson and other former Truman advisors.
Rallies in support of the troops were discouraged for fear that a patriotic response would lead to demands for victory and rollback. Military responsibility was divided among three generals so that no powerful theater commander could emerge to challenge Johnson as MacArthur had challenged Truman.
Nixon, who replaced Johnson in 1969, referred to his foreign policy as détente, a relaxation of tension. Although it continued to aim at restraining the Soviet Union, it was based on political realism, thinking in terms of national interest, as opposed to crusades against communism or for democracy. Emphasis was placed on talks with the Soviet Union concerning nuclear weapons called the Strategic Arms Limitation Talks. Nixon reduced U.S. military presence in Vietnam to the minimum required to contain communist advances, in a policy called Vietnamization. As the war continued, it grew less popular. A Democratic Congress forced Nixon, a Republican, to abandon the policy in 1973 by enacting the Case–Church Amendment, which ended U.S. military involvement in Vietnam and led to successful communist invasions of South Vietnam, Laos, and Cambodia.

Afghanistan: President Jimmy Carter came to office in 1977 and was committed to a foreign policy that emphasized human rights. However, in response to the Soviet invasion of Afghanistan, containment was again made a priority. The wording of the Carter Doctrine (1980) intentionally echoed that of the Truman Doctrine.

Reagan Doctrine: Following the communist victory in Vietnam, Democrats began to view further communist advances as inevitable, but Republicans returned to the rollback doctrine. Ronald Reagan, a long-time advocate of rollback, was elected U.S. president in 1980. He took a more aggressive approach to dealings with the Soviets and believed that détente was misguided and peaceful coexistence was tantamount to surrender. When the Soviet Union invaded Afghanistan in 1979, American policymakers worried that the Soviets were making a run for control of the Persian Gulf. Throughout the 1980s, under a policy that came to be known as the Reagan Doctrine, the United States provided technical and economic assistance to the Afghan guerrillas (mujahideen) fighting against the Soviet army.

After the Cold War: The conclusion of the Cold War in 1992 marked the official end of the containment policy, but the U.S. kept its bases in the areas around Russia, such as those in Iceland, Germany, and Turkey. Much of the policy later helped influence U.S.