Precommitments are most essential when we feel most compelled to break them. Constitutional law, our collective pact of precommitments, is never more important than in periods of crisis. History suggests that when democracies are captured by fear, they react in predictably troubling ways, in particular by targeting the most vulnerable for selective sacrifices that the majority would not likely be willing to endure if the sacrifices were evenly distributed. The Constitution is predicated on the paradoxical understanding that democracy’s defects can be offset by compelling the majority to adhere to certain norms precisely when the democratic process would categorically reject them.

If it is to function as a restraint on the politics of fear, the Constitution must be interpreted not only with an eye toward its purpose and history, but with an understanding of the profound pressures that are likely to be at play when a polity in fear demands action. Otherwise, the forces that favor repression within the ordinary political channels will infect constitutional law as well. Holding the line during security crises is no simple matter. One need only think of the Supreme Court’s shameful ratification of the internment of 120,000 Americans and immigrants of Japanese descent during World War II, or its validation of prosecutions for anti-war speech during World War I. Political repression during times of crisis is nearly always deeply regretted as a mistake after the fact. If we are to learn from such mistakes, constitutional law is the place to locate and instantiate those lessons, in the hope that the country will exercise restraint the next time around...