Federalism in the United States is the constitutional system that splits governing power between one national government and fifty state governments, giving each its own authority, its own officials, and its own courts, while making federal law supreme when the two levels genuinely conflict. The Constitution lists what the federal government may do, leaves everything else to the states or the people, and sets rules for what happens at the seams. Understanding the system means understanding three things: what each level can do on its own, how conflicts get resolved, and what limits keep either level from taking over the other’s work.
How the Constitution Divides Power
The federal government is a government of enumerated powers. It can only act where the Constitution authorizes it to act. Article I, Section 8 provides the main list: Congress can levy taxes, borrow money, regulate interstate and foreign commerce, coin money, establish post offices, declare war, and raise armies, among other functions.1Legal Information Institute. U.S. Constitution Annotated Article 1 Section 8 The same section contains the Necessary and Proper Clause, a catch-all that lets Congress pass laws needed to carry out those listed powers.2Constitution Annotated. ArtI.S8.C18.1 Overview of Necessary and Proper Clause
The clause has done heavy lifting since the country’s early years. In McCulloch v. Maryland (1819), Chief Justice Marshall upheld the creation of a national bank even though banking is nowhere in the Constitution, reasoning that “if the end be legitimate, and within the scope of the Constitution, all the means which are appropriate” and “not prohibited” may be used to achieve it.3Justia. McCulloch v Maryland, 17 US 316 (1819) The same case established that states cannot tax or otherwise interfere with legitimate federal operations. That combination — enumerated powers plus implied authority to carry them out — gives Congress room to address modern problems while keeping every federal action tied back to a constitutional grant.
Everything else belongs to the states or the people. The Tenth Amendment says so directly: powers not delegated to the federal government and not prohibited to the states are reserved.4Congress.gov. U.S. Constitution – Tenth Amendment In practice, states handle most of the governing people experience day to day. Under their inherent police power, states regulate public health, safety, welfare, and morals, and the Supreme Court has recognized that this authority reaches everything from land use and zoning to sanitation and law enforcement, while conceding that tracing its “outer limits is fruitless.”5Legal Information Institute. Police Powers Professional licensing sits with the states. So does running elections: the country has more than 10,000 separate election jurisdictions, and no two states administer the process the same way.6U.S. Election Assistance Commission. Who Is in Charge of Elections in My State?
Some powers belong to both levels at once. Taxation is the clearest example. Congress can lay and collect taxes to fund federal operations, and states retained their own taxing authority under the Tenth Amendment. That is why Americans pay federal income tax and, in most places, a separate state income or sales tax. Both levels also borrow money and run their own independent court systems, each with its own judges and jurisdiction. Infrastructure works the same way: the federal government funds interstate highways and sets national standards, while state and local governments build and maintain the roads people actually drive on. Neither level needs the other’s permission to tax, borrow, or build courts, which is what keeps the machinery working across a country of 330 million people.
When Federal and State Law Collide
The rule for conflicts is in Article VI. The Supremacy Clause declares that the Constitution, federal statutes, and treaties are “the supreme Law of the Land” and that state judges must follow them regardless of any conflicting state law.7Congress.gov. U.S. Constitution Article VI Clause 2 When federal and state law genuinely conflict, federal law wins. The mechanism is called preemption, and most of the day-to-day friction in federalism plays out here.8Constitution Annotated. ArtVI.C2.1 Overview of Supremacy Clause
Preemption takes a few forms. Express preemption happens when Congress writes language directly into a statute saying it overrides state law on the subject. Conflict preemption applies when a state law makes it impossible for someone to follow both federal and state requirements, or when the state law actively obstructs a federal objective. Field preemption applies when Congress has regulated an area so thoroughly that no room is left for state involvement, and courts infer Congress meant to occupy the entire field.8Constitution Annotated. ArtVI.C2.1 Overview of Supremacy Clause Industries that operate across state lines, like aviation and telecommunications, are frequent targets of field preemption because 50 different regulatory schemes would be unworkable. Once a state law is preempted, it becomes unenforceable, and continued enforcement can be halted by court injunction.
States face an additional restriction even when Congress has said nothing. Under what is called the Dormant Commerce Clause, states cannot pass laws that discriminate against or excessively burden interstate commerce, an implied limit drawn from the Commerce Clause itself.9Legal Information Institute. Dormant Commerce Clause A state safety regulation that incidentally raises costs for out-of-state truckers is one thing; a state law that effectively blocks out-of-state waste from entering its landfills is another. Courts weigh the local benefit against the burden on interstate trade, and lopsided burdens fall.10Justia. Pike v Bruce Church Inc, 397 US 137 (1970)
The Commerce Clause and the Reach of Federal Power
No single provision has done more to shape the modern balance than the Commerce Clause, which gives Congress power to regulate commerce “among the several States.” The Supreme Court has read the language broadly from the start. In Gibbons v. Ogden (1824), it struck down a New York steamboat monopoly and held that the commerce power “does not stop at the external boundary of a State” and “extends to every species of commercial intercourse” between states.11Justia. Gibbons v Ogden, 22 US 1 (1824)
The real expansion came in the twentieth century. Wickard v. Filburn (1942) upheld a federal wheat-production quota against a farmer who grew wheat only for personal use on his own farm. The Court reasoned that even though one farmer’s home-grown wheat has a trivial effect on the national market, the combined effect of many farmers doing the same thing is “far from trivial,” because that wheat displaces purchases they would otherwise make on the open market.12Justia. Wickard v Filburn, 317 US 111 (1942) This aggregation approach gave Congress reach into almost any economic activity, no matter how local it might appear in isolation.
The clause has a ceiling, though. In National Federation of Independent Business v. Sebelius (2012), the Supreme Court held that Congress cannot use the Commerce Clause to force people to enter commerce. The Affordable Care Act’s individual mandate, which required uninsured people to buy health coverage, crossed that line because “the power to regulate commerce presupposes the existence of commercial activity to be regulated.”13Justia. National Federation of Independent Business v Sebelius, 567 US 519 (2012) The mandate survived on other grounds as a tax, but the ruling clarified that Congress can regulate existing commercial behavior, not compel it.
Structural Limits on Federal Power Over the States
Preemption lets Congress override state law, but it does not let Congress turn state governments into enforcers of federal programs. That is the anti-commandeering doctrine, one of the most important structural protections in modern federalism. The Supreme Court has described the federal system as one in which the Framers rejected a national government that would “act upon and through the States,” choosing instead one where federal and state governments exercise “concurrent authority over the people” directly.14Justia. Printz v United States, 521 US 898 (1997)
The doctrine took shape in New York v. United States (1992), where Congress ordered states to either regulate radioactive waste according to federal specifications or take ownership of it. The Court struck the scheme down, holding that “Congress may not commandeer the legislative processes of the States by directly compelling them to enact and enforce a federal regulatory program.”15Justia. New York v United States, 505 US 144 (1992) Five years later, Printz v. United States (1997) extended the rule to state executive officials, striking down a Brady Act provision that required local law enforcement officers to conduct background checks on gun buyers. Justice Scalia wrote that “the Federal Government may neither issue directives requiring the States to address particular problems, nor command the States’ officers … to administer or enforce a federal regulatory program,” and that “no case-by-case weighing of the burdens or benefits is necessary” because the practice is “fundamentally incompatible with our constitutional system of dual sovereignty.”14Justia. Printz v United States, 521 US 898 (1997)
More recently, Murphy v. NCAA (2018) closed a loophole. A federal statute had barred states from authorizing sports gambling. The Court struck it down, reasoning that “the distinction between compelling a State to enact legislation and prohibiting a State from enacting new laws is an empty one. The basic principle—that Congress cannot issue direct orders to state legislatures—applies in either event.”16Supreme Court of the United States. Murphy v National Collegiate Athletic Association (2018) The practical result was the legalization of sports betting in dozens of states within a few years.
Anti-commandeering does not leave Congress powerless. It can regulate people and businesses directly through federal agencies. And it can pay states to cooperate, which is often the more effective tool.
The Spending Clause and Its Coercion Limit
Federal grants make up roughly a third of total state revenue, and that financial relationship gives Congress enormous practical leverage even in areas where it lacks direct regulatory authority. The Supreme Court set the ground rules in South Dakota v. Dole (1987), which upheld a federal law threatening to withhold a percentage of highway funding from any state that let people under 21 buy alcohol. Spending conditions must promote the general welfare, be stated unambiguously so states know what they are agreeing to, relate to a legitimate federal interest, and not themselves violate other constitutional provisions.17Justia. South Dakota v Dole, 483 US 203 (1987)
Financial pressure can still cross a line. The withholding in Dole was about 5% of highway funds, and the Court found it fell short of the “point at which pressure turns into compulsion.”17Justia. South Dakota v Dole, 483 US 203 (1987) In NFIB v. Sebelius, the Court held that threatening to cut all of a state’s Medicaid funding for refusing to expand the program was unconstitutionally coercive, because the sums were so large that no state could realistically say no.13Justia. National Federation of Independent Business v Sebelius, 567 US 519 (2012) Somewhere between 5% of highway funds and the entirety of Medicaid, encouragement becomes compulsion. Pinpointing that line remains one of the unsettled questions of federalism.
How States Relate to Each Other
Federalism is not only vertical. The Constitution also governs how states treat each other, and Article IV sets the ground rules.
Full Faith and Credit
Article IV, Section 1 requires every state to honor the “public Acts, Records, and judicial Proceedings of every other State.” A divorce decree issued in one state is valid in every other state, and a court judgment from one state can generally be enforced in another. The Supreme Court has been exacting about final judgments: states must give them conclusive effect so long as the original court had proper authority over the parties and the subject matter. The clause is less rigid about other states’ statutes, allowing states to apply their own law in many situations as long as they do not shut their courts entirely to claims arising under another state’s law.18Constitution Annotated. Overview of Full Faith and Credit Clause
Privileges and Immunities
Article IV, Section 2 provides that citizens of each state are entitled to the “Privileges and Immunities of Citizens in the several States.”19Congress.gov. U.S. Constitution Article IV Section 2 The purpose is to keep states from treating out-of-state residents as second-class citizens. A state generally cannot deny nonresidents access to its courts, charge them higher business licensing fees purely because of where they live, or bar them from earning a livelihood within its borders. The clause does not require perfect equality in every context, but it blocks discrimination against outsiders when fundamental economic and civil rights are at stake.
Extradition
Article IV, Section 2 also addresses fugitives. When someone charged with a crime in one state flees to another, the governor of the state where the fugitive is found must deliver that person back upon lawful demand. For over a century, states treated the obligation as merely moral. The Supreme Court reversed course in Puerto Rico v. Branstad (1987), holding that federal courts can compel a governor to fulfill the duty. The obligation is not absolute: if the fugitive is serving a sentence in the state where they were found, that state can finish enforcing its own laws first before handing the person over.20Legal Information Institute. Overview of the Extradition (Interstate Rendition) Clause
Interstate Compacts
States can enter formal agreements with one another, known as interstate compacts, to solve shared problems. Compacts cover everything from water rights to regional transit. Article I, Section 10 requires congressional approval when a compact would shift political power in a way that encroaches on federal authority; roughly 40% of existing compacts have needed that approval. The rest, dealing with matters that do not affect the federal balance, take effect without congressional involvement. These agreements are one of the clearest signs that states are independent political actors capable of cooperating on their own terms, not subordinate units waiting for Washington’s direction.