Judicial review has long been characterized by constitutional scholars as countermajoritarian and antidemocratic. This Article employs insights from political science and game theory to argue that the opposite is true: judicial review supports popular sovereignty by mitigating the principal-agent problem that lies at the heart of democratic government. In a system of constitutional government premised upon popular sovereignty, the government acts as the agent of the people and is supposed to exercise power consistent with the terms and conditions imposed by the people in the form of a constitution. But the interests of principal and agent may diverge: those entrusted with public power may seek to seize more power than has been given them, or to turn the power they have been given against the people themselves. The people thus face the challenge of asserting effective control over a potentially treacherous government, and they cannot meet this challenge without first overcoming two potentially serious obstacles. One is an information problem: the people cannot respond to bad behavior by the government if they remain unaware of that behavior. Another is a coordination problem: even if the people acting together are capable of replacing the government, such action may require widespread coordination that can be difficult to achieve. Courts that engage in judicial review perform monitoring and coordinating functions that help the people to solve both of these problems. First, a court engaged in judicial review serves the function of a whistleblower or fire alarm: it provides the people with reliable, low-cost information about whether their government has overstepped the bounds of its delegated power. Second, courts can coordinate popular action against usurping governments. People are unlikely to act openly against a tyrannical government unless they believe that others will act as well. They are therefore in need of a highly public signal that creates such beliefs on a large scale. A court can provide such a signal by ruling publicly against the government. The fact that constitutional courts perform monitoring and coordinating functions helps, in turn, to solve the puzzle of why governments obey them, notwithstanding the fact that they lack the power of either the purse or the sword. The ability of a court to mobilize the people against the government means that government disobedience of the court's decisions carries potentially severe consequences. This account has important empirical implications that directly contradict the conventional wisdom about the purported relationship between judicial legitimacy and judicial power. It is often thought that courts jeopardize their legitimacy, and thus their power, by rendering unpopular decisions. This Article argues that the opposite may be true. When a court renders an unpopular decision that nevertheless receives widespread compliance, it generates and reinforces strategic expectations about its efficacy in future cases. Thus, the successful exercise of judicial power in the face of opposition or criticism merely begets even more judicial power. The overall theory also helps to explain both judicial independence and public support for the courts in the face of decisions that may sometimes defy the wishes of a majority: because constitutional courts perform a watchdog function, the people have reason to support their independence even if specific judicial decisions happen to be unpopular.

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