Initially, the U.S. Supreme Court interpreted the reasonableness standard of the Fourth Amendment as imposing a presumptive warrant requirement, stating that “searches conducted outside the judicial process without prior approval by judge or magistrate are per se unreasonable under the Fourth Amendment — subject only to a few specifically established and well delineated exceptions.” The Court, however, has wavered from this approach, determining that “a warrant is not required to establish the reasonableness of all government searches; and when a warrant is not required . . . probable cause is not invariably required either.”