Federalism: How Power Is Divided Between the Nation and the States
The United States has two levels of government operating over the same territory and the same people at the same time. A resident of any state lives under both a state constitution and the federal Constitution, pays two sets of taxes, and can be prosecuted in either of two court systems. That arrangement is federalism, and a large share of the Constitution is occupied with sorting out which government may do what.
The sorting was not tidy in 1787 and it is not tidy now. What follows describes the pieces the document actually supplies, along with the disagreement about their reach that has run without pause since the First Congress.
Enumerated, Reserved, and Concurrent Powers
The federal government is a government of enumerated powers. It holds the authorities the Constitution grants it, not a general power to govern. Most of those grants sit in Article I, Section 8: taxing and spending, borrowing, regulating commerce, setting uniform rules of naturalization and bankruptcy, coining money, establishing post offices, granting patents and copyrights, declaring war, raising and supporting armies, and providing a navy, among others.
The Tenth Amendment states the other side of the ledger: “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.” States hold what is usually called the police power, the general authority over health, safety, and welfare that the federal government was never given. Most criminal law, family law, property and contract law, schooling, professional licensing, and local government are state matters for that reason.
A third category is concurrent: powers both levels hold at once. Both may tax, borrow, build roads, run court systems, and maintain police forces. The Constitution assumes this overlap rather than resolving it.
The Necessary and Proper Clause
Article I, Section 8 closes with the authority to make all laws “necessary and proper for carrying into Execution the foregoing Powers.” How much that adds was contested almost immediately, in the argument over whether Congress could charter a national bank when no clause anywhere mentions banks.
The Supreme Court took the broader view in McCulloch v. Maryland (1819), reading “necessary” to mean useful or appropriate rather than strictly indispensable:
Let the end be legitimate, let it be within the scope of the constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the constitution, are constitutional.
The same decision held that Maryland could not tax the federal bank, on the ground that a state may not tax an instrument of the national government. Both halves of the case are still cited constantly.
The Commerce Clause
Congress may “regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes.” That short clause carries an enormous share of modern federal law. Its first major construction came in Gibbons v. Ogden (1824), which treated commerce as including navigation and held that a state-granted steamboat monopoly could not stand against a federal licensing statute.
How far “among the several States” reaches, and in particular whether it covers activity that is local in itself but affects a national market, is one of the oldest live questions in American law. The Court’s answers have moved in both directions across two centuries. The Constitution Annotated collects that case law clause by clause and is the most direct way to follow it.
The Supremacy Clause
Article VI supplies the tie-breaker. The Constitution, federal laws made in pursuance of it, and treaties are “the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.”
Two points are easy to miss. The clause binds state judges directly, which is why state courts decide federal questions every day. And it protects only federal law made in pursuance of the Constitution, so it settles conflicts rather than granting Congress any new power. When valid federal law and state law genuinely collide, the state law yields, a result lawyers call preemption. The same article requires officials at both levels to swear an oath to the Constitution and forbids any religious test for federal office. Article VI can be read in full at the National Archives.
Anti-Commandeering
A related rule concerns what the federal government may demand of state governments themselves. Congress may regulate individuals directly, and it may offer states money on conditions. What the Supreme Court has said it may not do is compel a state to legislate or to administer a federal program.
Two decisions made the point. New York v. United States (1992) struck down a provision requiring states either to regulate radioactive waste as Congress directed or to take ownership of it. Printz v. United States (1997) held that Congress could not require local law enforcement officers to carry out background checks under a federal firearms statute. The reasoning in both was structural: accountability blurs when one government can order another government’s officials to act, because voters cannot tell whom to hold responsible. Cornell Law School’s annotated text of the Constitution is a convenient place to read the clauses involved.
What the States Owe One Another
Article IV handles the horizontal relationships. States must give “Full Faith and Credit” to each other’s public acts, records, and judicial proceedings, which is why a judgment entered in one state is generally honored in another. Citizens of each state are entitled to “all Privileges and Immunities of Citizens in the several States,” barring a state from treating out-of-staters worse in basic respects. Article IV also governs the admission of new states and guarantees every state a republican form of government.
A Disagreement That Has Not Ended
The balance has shifted over time, and the reasons are more textual than they may appear. The Reconstruction Amendments of 1865 to 1870 gave Congress explicit power to enforce new national guarantees against the states, a change covered on our amendments page. The Sixteenth and Seventeenth Amendments, both ratified in 1913, altered federal finance and the Senate’s relationship to state legislatures.
On the reach of federal power today, two readings are held seriously and in good faith. One holds that the enumerated powers, read in light of the purposes they serve and the conditions of a genuinely national economy, support broad federal legislation, and that the Tenth Amendment restates what was not granted rather than imposing an independent limit. The other holds that enumeration means nothing unless some subjects fall outside it, that a general federal police power was deliberately withheld, and that structural rules such as anti-commandeering are the practical expression of that choice. This publication describes both and adjudicates neither. How such disputes get argued is the subject of our page on constitutional interpretation, and the overview of the document shows where each clause sits.