Why has U.S. national security policy scarcely changed from the Bush to the Obama administration? And why does it matter? The theory of "double government" posed by the nineteenth-century English scholar Walter Bagehot suggests a disquieting answer. The public is encouraged to believe that the visible, "Madisonian institutions"-the presidency, Congress, and the courts-make security policy. That belief sustains these institutions' legitimacy. Yet their authority is largely illusory. Presidential control is nominal, congressional oversight is dysfunctional, and judicial review is negligible. National security policy is made, instead, by a "Trumanite network" of several hundred members that is largely concealed from public view. These officials manage the military, intelligence, diplomatic, and law enforcement agencies that are responsible for protecting the nation. Their primacy is the result not of some nefarious or even purposeful plotting, but rather of structural incentives imbedded deep within the American political system. The Trumanites provide needed expertise, quick-footedness, institutional memory, and policy stability. Their ascendancy is the main reason for the continuity of national security policy. Yet the Trumanites' dominance threatens democratic accountability, for the U.S. Constitution's restraints operate primarily upon the hollowed-out Madisonian institutions, not the Trumanite network. The press and public opinion cannot fill the void; both are too manipulable, and their vitality depends upon robust Madisonian institutions powered by an informed and engaged electorate. Instead, widespread political ignorance prevails-and becomes more acute as Madisonian influence declines. The net result is a secretive, unrestrained, and expanding security apparatus that poses a grave threat to democracy.