The Court has stated repeatedly that searches conducted without a warrant are presumptively “unreasonable” and, accordingly, are presumptive violations of the Fourth Amendment. Although one can argue whether the Court truly enforces a “warrant requirement”—see Justice Thomas’s dissent in Groh v. Ramirez below—one cannot deny the importance of valid warrants to a huge range of police conduct. For example, absent exceptional circumstances (such as officers chasing a fleeing felon), police normally must have a valid warrant to search a residence without the occupant’s permission.
To be valid, a warrant must obey the Fourth Amendment’s command that “no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” This portion of the Amendment is known as the “Warrant Clause.” It requires: (1) that the evidence presented to the issuing judge or magistrate be sufficient to qualify as “probable cause,” (2) that the officers bringing the evidence to the judge or magistrate swear or affirm that the evidence is true to the best of their knowledge, (3) that the warrant specify where officers can search, and (4) that the warrant specify what things or persons officers may look for and may seize if found.
In addition, the Court has held that only a “neutral and detached magistrate” may issue a warrant. See Coolidge v. New Hampshire, 403 U.S. 443 (1971). That means the judge or magistrate must be independent of law enforcement; a state attorney general cannot issue warrants. In Connally v. Georgia, 429 U.S. 245 (1977), the Court held that a justice of the peace who received payment upon issuing a warrant, but no fee upon denying a warrant application, was not “neutral and detached.”