A few nightmare scenarios haunt the dreams of civil libertarians—scenes drawn from our long and ignominious history of intelligence abuses. One—call it the Nixon scenario—is that the machinery of the security state will fall into the hands of an autocratic executive, disdainful of the rule of law, who equates “national security” with the security of his own grip on political authority, who is all too willing to turn powers meant to protect us from foreign adversaries against his domestic political opponents, and who lacks any qualms about quashing inquiries into his own illegal conduct or that of his allies. Another—call it the Hoover scenario—is that the intelligence agencies anxious to protect their own powers and prerogatives will themselves slip the leash, using their command of embarrassing secrets to intimidate (and in extreme cases perhaps even select) their own nominal masters. As the American surveillance state has ballooned over the past 15 years, we’ve often invoked those scenarios to argue out that the slippery slope from a reasonable-sounding security measure a tool of anti-democratic repression is disquietingly short and well-oiled. You may trust that some new authority will only be used to monitor terrorists today, but under a more authoritarian administration, might it be used to suppress dissent—as when civil rights and anti-war activists became the targets of the FBI’s notorious COINTELPRO? You may be reassured by all the rigid rules and layers of oversight designed to keep the Intelligence Community accountable, but will those mechanisms function if the intelligence agencies decide to use their broad powers to cow their own overseers?