T he Constitution establishes a "system of dual sovereignty between the States and the Federal Government," with each state having its "own government," "endowed with all the functions essential to separate and independent existence." As the Supreme Court has recognized, states "possess sovereignty concurrent with that of the Federal Government, subject only to limitations imposed by the Supremacy Clause," the provision of the Constitution that makes federal law the "supreme Law of the Land" and prohibits states from contravening lawful enactments of Congress. Although the Supremacy Clause grants Congress a degree of authority to "impose its will on the States," the federal government may not exceed "the powers granted it under the Constitution." The Constitution only endows the federal government with a "limited" and "defined" set of enumerated powers, while reserving most other powers to the states. The various principles that delineate the proper boundaries between the powers of the federal and state governments are collectively known as "federalism," a doctrine based on the Framers' conclusion that allocating "powers between the National Government and the States enhances freedom, first by protecting the integrity of the governments themselves, and second by protecting the people, from whom all governmental powers are derived." The report then discusses "internal" limitations on Congress's exercise of several of its enumerated powers, including its spending and commerce powers, its authority to enact certain types of legislation to implement international treaties, its enforcement authority under the Civil War Amendments, and its powers under the Necessary and Proper Clause. Second, beyond the internal limits on Congress's powers, the Constitution also imposes "external" constraints on congressional action—that is, affirmative prohibitions found elsewhere in the text or structure of the document. Regulating Activities that Substantially Affect Interstate Commerce

Finally, Congress possesses the constitutional authority to regulate "activities that substantially affect interstate commerce." The Supreme Court, applying these factors, has periodically ruled that Congress may not invoke the Commerce Clause to regulate certain purely intrastate non-economic activities. Necessary and Proper Clause

Supplementing Congress's enumerated powers is the Necessary and Proper Clause, which grants Congress the power to "make all Laws which shall be necessary and proper for carrying into Execution the" powers enumerated in Article I of the Constitution, as well as "all other Powers vested by the Constitution in the Government of the United States, or in any Department or Officer thereof." External Federalism Limitations on Congress's Powers

In addition to the "internal" limitations on Congress's powers discussed above, the Supreme Court has recognized a variety of federalism doctrines that affirmatively prohibit Congress from taking certain actions even if Congress would otherwise be authorized to act pursuant to one of its enumerated powers. The Eleventh Amendment and State Sovereign Immunity

In addition to the aforementioned external constraints on Congress's power, the Eleventh Amendment to the United States Constitution—which states that "the Judicial power of the United States shall not be construed to extend to any suit in law or equity, commenced or prosecuted against one of the United States by Citizens of another State, or by Citizens or Subjects of any Foreign State"—establishes additional limitations on the federal government's power vis-à-vis the states. The Eleventh Amendment thereby implicates federalism by limiting the federal government's ability to regulate the states and thereby restricting Congress's authority to enact statutes that subject states to suit. As a result, a lawsuit against that officer effectively constitutes a suit against an individual rather than the state itself. The equal sovereignty principle thereby limits Congress's ability to enact legislation that subjects different states to unequal burdens.
The U.S. Constitution establishes a system of dual sovereignty between the states and the federal government, with each state having its own government, endowed with all the functions essential to separate and independent existence. Although the Supremacy Clause of the Constitution designates "the Laws of the United States" as "the supreme Law of the Land," other provisions of the Constitution—as well as legal principles undergirding those provisions—nonetheless prohibit the national government from enacting certain types of laws that impinge upon state sovereignty. The various principles that delineate the proper boundaries between the powers of the federal and state governments are collectively known as "federalism." Federalism-based restrictions that the Constitution imposes on the national government's ability to enact legislation may inform Congress's work in any number of areas of law in which the states and the federal government dually operate.
There are two central ways in which the Constitution imposes federalism-based limitations on Congress's powers. First, Congress's powers are restricted by and to the terms of express grants of power in the Constitution, which thereby establish internal constraints on the federal government's authority. The Constitution explicitly grants Congress a limited set of carefully defined enumerated powers, while reserving most other legislative powers to the states. As a result, Congress may not enact any legislation that exceeds the scope of its limited enumerated powers. That said, Congress's enumerated powers nevertheless do authorize the federal government to enact legislation that may significantly influence the scope of power exercised by the states. For instance, subject to certain restrictions, Congress may utilize its taxing and spending powers to encourage states to undertake certain types of actions that Congress might otherwise lack the constitutional authority to undertake on its own. Similarly, the Supreme Court has interpreted the Constitution's Commerce Clause to afford Congress substantial (but not unlimited) authority to regulate certain purely intrastate economic activities that substantially affect interstate commerce in the aggregate. Congress may also enact certain types of legislation in order to implement international treaties. Additionally, pursuant to a collection of constitutional amendments ratified shortly after the Civil War, Congress may directly regulate the states in limited respects in order to prevent states from depriving persons of certain procedural and substantive rights. Finally, the Necessary and Proper Clause augments Congress's enumerated powers by empowering the federal government to enact laws that are "necessary and proper" to execute its express powers.
In addition to the internal constraints on Congress's authority, the Constitution also imposes external limitations on Congress's powers vis-à-vis the states—that is, affirmative prohibitions on certain types of federal actions found elsewhere in the text or structure of the Constitution. The Supreme Court has recognized, for instance, that the national government may not commandeer the states' authority for its own purposes by forcing a state's legislature or executive to implement federal commands. Nor may Congress apply undue pressure to coerce states into taking actions they are otherwise disinclined to take. Furthermore, the principle of state sovereign immunity—which limits the circumstances in which a state may be forced to defend itself against a lawsuit against its will—imposes significant constraints on Congress's ability to subject states to suit. Finally, the Supreme Court has recognized limits to the extent to which Congress may subject some states to more onerous regulatory burdens than other states.