A deeply researched, fully updated edition of The National Security Constitution that explores the growing imbalance of institutional powers in American foreign affairs and national security policy Since the beginning of the American Republic, a package of norms has evolved in the U.S. Constitution to protect the operation of checks and balances in national security policy. This “National Security Constitution” promotes shared powers and balanced institutional participation in foreign policymaking. Today it is under attack from a competing claim of executive unilateralism generated by recurrent patterns of presidential activism, congressional passivity, and judicial tolerance. This dynamic has pushed presidents of both parties to press the limits of law in foreign affairs. In his award-winning National Security Constitution (1990), Harold Hongju Koh traced the evolution of this constitutional struggle across America’s history. This new book, based on the earlier volume but with roughly 70 percent new material, brings the story to the present, placing recent events into constitutional perspective. Reviewing the presidencies of the twenty-first century, he explains why modern national security threats have given presidents of both parties incentives to monopolize foreign policy decision-making, Congress incentives to defer, and the courts reasons to rubber-stamp. Koh suggests both a workable strategy and crucial prescriptions to restore the balance of our constitutional order in addressing modern global crises.