The Truman doctrine was the USAs change in foreign policy from isolationism to containment this meant instead of trying not to be involved in other counties affairs they actively began to protect states ( like Greece and South Korea) from a communist takeover. Churchill called the Truman doctrine and Marshall aid plan "two halves of the same walnut" as they went hand in hand. The Marshall aid plan was and injection of $16 billion dollars into the Western European economy this was bound to contain communism as communism thrives in poverty and squalor which was being tackled by the investment of Americas money. So they would not have been possible without one another.
