Until the 1948–1949 Berlin blockade, the United States had not decided whether U.S. forces should remain in West Berlin after the establishment of a West German government. But after the Soviet Union closed off surface routes to West Berlin, the Truman administration embarked on a massive airlift and established a de facto commitment to preserve the western sectors' independence. The U.S. guarantee to West Berlin is difficult to explain from the standpoint of realist theories of foreign policymaking. Realism maintains that leaders should undertake commitments only if adequate power is available and that ends should be commensurate with means. West Berlin was indefensible, and its access routes could be restricted at any time. Only by analyzing the decision-making process from the standpoint of political psychology can scholars determine why U.S. policymakers acted as they did. President Harry Truman played a pivotal role in decision-making in Berlin, and he relied on his own judgment rather than policy analysis. Psychological research on intuitive judgment indicates that people sometimes make important decisions without deliberating when the problem is highly complex and the outcome uncertain—precisely the conditions Truman faced in 1948.