Judicial review.
The way the Constitution is understood is influenced by court decisions, especially those of the Supreme Court. These decisions are referred to as precedents. Judicial review is the power of the Court to examine federal legislation, federal executive, and all state branches of government, to decide their constitutionality, and to strike them down if found unconstitutional.
Judicial review includes the power of the Court to explain the meaning of the Constitution as it applies to particular cases. Over the years, Court decisions on issues ranging from governmental regulation of radio and television to the rights of the accused in criminal cases have changed the way many constitutional clauses are interpreted, without amendment to the actual text of the Constitution.
Legislation passed to implement the Constitution, or to adapt those implementations to changing conditions, broadens and, in subtle ways, changes the meanings given to the words of the Constitution. Up to a point, the rules and regulations of the many federal executive agencies have a similar effect. If an action of Congress or the agencies is challenged, however, it is the court system that ultimately decides whether these actions are permissible under the Constitution.
The Supreme Court has indicated that once the Constitution has been extended to an area (by Congress or the Courts), its coverage is irrevocable. To hold that the political branches may switch the Constitution on or off at will would lead to a regime in which they, not this Court, say "what the law is".
Scope and theory.
Courts established by the Constitution can regulate government under the Constitution, the supreme law of the land. First, they have jurisdiction over actions by an officer of government and state law. Second, federal courts may rule on whether coordinate branches of national government conform to the Constitution. Until the twentieth century, the Supreme Court of the United States may have been the only high tribunal in the world to use a court for constitutional interpretation of fundamental law, others generally depending on their national legislature.
The basic theory of American Judicial review is summarized by constitutional legal scholars and historians as follows: the written Constitution is fundamental law. It can change only by extraordinary legislative process of national proposal, then state ratification. The powers of all departments are limited to enumerated grants found in the Constitution. Courts are expected (a) to enforce provisions of the Constitution as the supreme law of the land, and (b) to refuse to enforce anything in conflict with it.
In Convention. As to judicial review and the Congress, the first proposals by Madison (Va) and Wilson (Pa) called for a supreme court veto over national legislation. In this it resembled the system in New York, where the Constitution of 1777 called for a "Council of Revision" by the Governor and Justices of the state supreme court. The council would review and in a way, veto any passed legislation violating the spirit of the Constitution before it went into effect. The nationalist's proposal in Convention was defeated three times, and replaced by a presidential veto with Congressional override. Judicial review relies on the jurisdictional authority in Article III, and the Supremacy Clause.
