major casualties, severe economic loss, and social disruption.¹ The danger of future terrorist attacks on the United States is both real and serious.

At the same time, inappropriate or disproportionate responses to the terrorist threat also pose serious dangers to society. History demonstrates that measures taken in the name of improving national security, especially in response to new threats or crises, have often proven to be both ineffective and offensive to the nation’s values and traditions of liberty and justice.² So the danger of unsuitable responses to the terrorist threat is also real and serious.

Given the existence of a real and serious terrorist threat, it is a reasonable public policy goal to focus on preventing attacks before they occur—a goal that requires detecting the planning for such attacks prior to their execution. Given the possibility of inappropriate or disproportionate responses, it is also necessary that programs intended to prevent terrorist attacks be developed and operated without undue compromises of privacy.

Premise 2. The terrorist threat to the United States, serious and real though it is, does not justify government authorities conducting activities or operations that contravene existing law.

The longevity of the United States as a stable political entity is rooted in large measure in the respect that government authorities have had for the rule of law. Regardless of the merits or inadequacies of any legal regime, government authorities are bound by its requirements until the legal regime is changed, and, in the long term, public confidence and trust in government depend heavily on a belief that the government is indeed adhering to the laws of the land. The premises above would not change even if the United States were facing exigent circumstances. If existing legal authorities (including any emergency action provisions, of which there are many) are inadequate or unclear to deal with a given situation