How did the strategy of containing communism evolve during the Truman and Eisenhower administration?

The cornerstone of the policy of containment came when George F. Kennan sent his "long telegram" from the U.S. embassy in Moscow in 1946.  The document contained a clear message that the Soviet Union was inherently insecure and expansionist, and that ultimately Soviet leaders wanted to control their neighboring countries to shield themselves from traditional enemies. Ultimately, Kennan argued, the Soviets wanted to overthrow western governments.

The thesis laid out by Kennan took hold in Washington, where the Truman administration began to take a bolder stance against the Soviet Union.  For example, he promised aid to all those countries who worked to resist communist influence.

The idea of containment, as Kennan argued later in his life, was eventually expanded beyond what he had argued. Kennan was a believer in diplomatic and political containment and pressure, not necessarily military containment. But when Eisenhower reached office, he began a huge build up of nuclear weapons, aimed squarely at containing the Soviet Union.

It was remarkable, at the time, how quickly after the war ended that the United States and the Soviet Union became locked in a cold war that would last for decades.