The history of liberty, Justice Felix Frankfurter once noted, has largely been the history of observance of procedural safeguards and the history of the destruction of liberty, Professor Anthony Amsterdam has added, has largely been the history of the relaxation of those safeguards in the face of plausible sounding governmental claims of a need to deal with widely frightening and emotion freighted threats to the good order of society. These plausible-sounding government claims are being heard today -and they are putting enormous pressure on the Fourth Amendment, the constitutional provision that protects the right of the people to be secure in their persons, homes, papers, and effects, against unreasonable searches and seizures and...