In the span of just a few years, the U.S. Supreme Court has brought the venerable constitutional concept of federalism back to life with a vengeance. In the 1999 Term alone, the Rehnquist Court struck down three federal laws for violating basic principles of federalism and narrowly construed a fourth to avoid any conflict with those precepts. When viewed in conjunction with the Court's other recent defenses of federalism ideals, this activity takes on historic proportions: in the past five years, the Rehnquist Court has struck down 23 federal laws, including 11 for exceeding Congress' authority under the U.S. Commerce Clause, §5 of the Fourteenth Amendment, or both. Not since the titanic conflict between Congress and the Court in the 1930s over the fate of the New Deal has the Court been as active as it has in recent years in enforcing federalism-based limitations on congressional power.

The implications of the Court's recent federalism decisions have been the subject of considerable speculation, particularly with respect to their likely impact on areas in which the Congress frequently or routinely uses its powers under the Commerce Clause and §5 of the Fourteenth Amendment. Perhaps no area has been the focus of more concern than environmental law, the field in which Congress arguably moit frequently resorts to its Commerce Clause power. Though none of the Court's federalism decisions over the past five years involved challenges to federal environmental regulations, the opinions gave no indication of any field exempted from the application of their reasoning. Indeed, if there were any doubt about the Court's willingness to confront the implications of its recent federalism decisions for environmental law, it resolved them in one of its last decisions of the 1999 Term. Just before the end of the Term, the Court, in Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC), agreed to hear a constitutional challenge to the U.S. Environmental Protection Agency's (EPA's) and the U.S. Army Corps of Engineers' migratory bird rule, which prohibits the destruction of any wetlands, including isolated ones, that are likely to be or actually are frequented by migratory birds. Together with these agencies' broad assertion of federal jurisdiction of any waters that "could affect" interstate commerce, the rule has generated considerable controversy as impediments to commercial and other development on private property with no apparent or direct connection to interstate waterways. Thus, in agreeing to hear a constitutional challenge to this rule, the Court will have a critical opportunity to clarify the implications of its recent federalism decisions for what is commonly perceived as the federal government's most aggressive effort to protect the quality of the nation's waters.