In June 1949, the director of the State Department's Policy Planning Staff, George Kennan, twice brought theologian Reinhold Niebuhr to the group's meetings as a consultant. Niebuhr returned to speak to the State Department many times during the Truman administration, and was joined in doing during the so by arch-realist political scientist Hans Morgenthau. According to an attendee at one of the sessions, Niebuhr's "position was to promote all possible international cooperation and organization, but not to allow utopian visions of world government to interfere with the complicated task of securing the precarious order and justice that were available within the existing system." That is about as succinct a definition of foreign-policy realism as it is possible to get.
With Kennan, Niebuhr, and Morgenthau all pioneers of this approach to international affairs, those meetings were arguably the high-water mark for realist thinkers in the upper echelons of a Democratic administration. But they were hardly the only times liberals and realists have found profit in allying. And with today's Republican Party relying almost exclusively on neoconservatives to set its foreign-policy agenda, realists are once again starting to move toward the Democratic Party.
Realism is widely thought to be antithetical to liberalism. This school of thought in American foreign policy emerged in the first place as a reaction against the reckless naivete of that exemplar of progressivism, Woodrow Wilson. As Morgenthau wrote in his 1948 book Politics Among Nations, a foundational text for realists, Wilson's pledge to make the world safe for democracy, his promises to support self-determination for all peoples, and his endeavors to make the League of Nations the guarantor of world peace were the very embodiment of utopianism. Certainly the self-righteous Wilson would have found blasphemous the basic postulates of realism: power is the driving force in the world, the international system is impossible to harmonize, stability requires a balance of power, and no country is innocent.
Yet while Wilson unfailingly couched his actions in moralistic language, his decision to involve America in World War I in 1917--rather than much sooner, as Theodore Roosevelt urged--can be seen as a classic realist maneuver. After letting the combatants exhaust themselves for three years while sitting on the sidelines and preserving its power, America intervened to prevent a hostile power--Germany--from rearranging the Europe balance of power in its favor. In his realist manifesto U.S. Foreign Policy: Shield of the Republic, journalist Walter Lippman, who served in the Wilson administration as an adviser, wrote that the "undeclared" reason for American involvement was that "many Americans saw in 1917 that if Germany won, the United States would have to face a new and aggressively expanding German empire which had made Britain, France, and Russia its vassals, and Japan its ally." In the Great War, "Wilson's idealistic vision coexisted with geopolitical realism," as the journalist-historian Michael Lind put it in his book The American Way of Strategy.
After securing victory for the Allies, however, Wilson jettisoned any semblance of realism and instead embraced a quixotic attempt to remake the world along the lines of universal justice. His Republican successors Harding and Coolidge erred in the opposite direction: they withdrew America from involvement in European affairs, ignoring realist principles by permitting Germany to rearm. As Kennan argued in his classic work American Diplomacy, 1900-1950, "It [is] essential to us, as it was to Britain, that no single continental land power should come to dominate the entire Eurasian land mass." Such a power would inevitably embark upon an overseas expansion that would jeopardize American security with all the resources of the interior of Europe and Asia, Kennan wrote.
It would take the paradigmatic Democratic president of the 20th century to prevent this. …