Over the past few decades, the world has experienced considerable change. Most momentous was the collapse of the Soviet Union and communism throughout Eastern Europe. Will the twenty-first century witness the triumph of capitalism, democracy, and 'Westernization' throughout the world? Or will it see a clash of civilizations and coming anarchy? And what of the United States, the pre-eminent power at the turn of the century. What leadership role will it play in the twenty-first century? Many assume that it will, indeed that it should, assume a strong leadership role. Disagreement is usually about which goals an activist United States should pursue abroad and whether United States leadership should be unilateral or multilateral. The debate often revolves around the opportunities for and constraints on United States leadership posed by the international system. Questions have been raised about the extent to which the United States is capable of exercising global leadership, given the relative decline of American power in recent years. Some argue in favour of American renewal. Yet the dialogue largely ignores the role of internal politics in the making of United States foreign policy -- and herein lies the key to the future of American leadership in the post-Cold War world. Most Americans believe that foreign policy is the purview of the president. This perception is reinforced by the majority of commentators and analysts of global affairs, who tend to simplify the American political process by equating 'the president' with 'United States foreign policy,' and in the process understate and ignore the 'politics' of United States foreign policy. The key question for the twenty-first century may very well have to do with the extent to which the United States can occupy a leadership role. Or, more accurately, the extent to which a president can govern and lead United States foreign policy into the future. The answer is critical and more complex then most realize. It is embedded in politics and is the focus of this article. THE DOMESTIC POLITICAL LANDSCAPE The president is the most powerful political actor in the United States. He has many constitutional roles and holds many positions that contribute to his power. Among the most important of these are commander-in-chief, chief diplomat, chief administrator, chief-of-state, chief legislator, voice of the people, and chief judicial officer.(f.1) However, the president also faces many constraints and uncertainties that limit his power. In the constant struggle to exercise power successfully, the president is limited by time (too little) and information (too much and too little). Institutional constraints include an entrenched bureaucracy, an independent Congress, state and local governments, political parties, and interest groups and social movements. Other uncertain elements -- the courts, public opinion, the media, and the larger global environment -- at times may enhance his power and at other times may act to constrain it. Because of these constraints and uncertainties the president often finds that he has great difficulty in successfully implementing his policies. When all is said and done, presidents face a 'paradox of power': on the one hand, the president is an extremely powerful actor; on the other hand, relative to the rest of government, the society, and the environment, he faces many constraints on successfully exercising power.(f.2) Clearly, the president is not nearly as powerful as many people assume. President John F. Kennedy understood this when he said that the president 'is rightly described as a man of extraordinary powers. Yet it is also true that he must wield those powers under extraordinary limitations.'(f.3) It is also important to remember that the presidency usually has its own 'life cycle': presidents are strongest when they enter office and their power tends to decline over time.(f.4) Thus, although the president of the United States is powerful, his power is not so great as the popular stereotype would have it, even in the area of foreign policy. …