Federalism affects policy making by dividing authority between Congress and the states, letting federal law override state law when they conflict, giving Washington leverage through the money it distributes, and leaving states free to set their own rules in the wide space federal law doesn’t fill. That split is why a single issue can look completely different depending on which level of government is acting, and why so much policy fighting is really a fight over who gets to decide.
Who Gets to Decide What
Article I, Section 8 of the Constitution lists the powers Congress holds: coining money, declaring war, regulating interstate commerce, taxing and spending for the general welfare, and a handful of others.1Congress.gov. Constitution Annotated – Article I Section 8 Anything not on that list, and not otherwise forbidden, belongs to the states or the people under the Tenth Amendment.2Congress.gov. Tenth Amendment States use that reserved authority to run schools, license professions, set most criminal penalties, manage public health programs, and regulate land use.
This division decides who gets the first word on a policy question, and often the last. Congress can set a national minimum wage under its commerce power. It cannot dictate a state’s elementary school curriculum. A state can ban a pesticide inside its borders. It cannot print currency. The line between the two isn’t always obvious, and the arguments over where it falls drive some of the biggest policy debates in the country.
Congress Cannot Force States to Enforce Federal Law
Even when Congress clearly has authority to regulate something, it cannot make state governments do the regulating for it. The Supreme Court set this rule in New York v. United States (1992), holding that Congress cannot order states to enact or administer a federal program, and extended it in Printz v. United States (1997), which barred Congress from conscripting individual state officers into federal enforcement.3Constitution Annotated. Amdt10.4.2 Anti-Commandeering Doctrine
The policy consequences are real. If Congress wants a federal program enforced nationwide, it has to build its own administrative machinery or offer states enough to bring them in voluntarily. Immigration is the recurring flashpoint: the federal government writes immigration law, but it cannot force local police departments to carry out deportation-related tasks. That choice, between building federal capacity and persuading states to cooperate, shapes how far any given policy actually reaches.
When Federal Law Overrides State Law
When federal and state laws collide, federal law wins. The Supremacy Clause in Article VI makes the Constitution and federal statutes made under it “the supreme Law of the Land,” binding on every state judge regardless of any contrary state law.4Constitution Annotated. Constitution of the United States – Article VI That clause does more than pick a winner in individual disputes. It lets Congress preempt entire areas of state regulation.
Preemption comes in different flavors. Sometimes Congress says outright that a federal statute overrides state law on a particular topic. Sometimes courts infer preemption because Congress has occupied a field so completely that no room is left, or because complying with both laws at once is impossible.5Congress.gov. Federal Preemption – A Legal Primer Nuclear safety and immigration are two areas where federal authority is treated as dominant enough to squeeze out state rules.
The decision to preempt is itself a major policy choice. When Congress preempts, it imposes a single national rule. When it doesn’t, states are free to vary. Industries and advocacy groups spend heavily fighting over which way that switch gets flipped, because the answer determines whether they face one rulebook or fifty.
Where Both Governments Regulate at Once
A lot of powers are not exclusive to either level. Both Congress and state legislatures can tax, build infrastructure, establish courts, and pass criminal laws. These concurrent powers produce the most tangled policy dynamics in the system, because both levels are acting in the same space at the same time.
The result is layered regulation. A business owes federal income tax and state income tax. A factory answers to both EPA rules and a state environmental agency. A worker’s paycheck sits under both federal and state wage law. Where those rules conflict, the Supremacy Clause resolves the conflict for the federal side, but only if the federal law is itself constitutional.4Constitution Annotated. Constitution of the United States – Article VI Where they don’t conflict, both apply, which is why people and businesses often navigate two full regulatory systems at once.
How Congress Shapes State Policy Without Regulating Directly
Congress doesn’t have to regulate to change what states do. The taxing and spending power gives it enormous leverage, because it distributes hundreds of billions of dollars in grants each year and almost always attaches conditions to the money.
Grants With Strings
Categorical grants fund narrowly defined programs and usually require states to follow detailed federal rules and put up matching funds. Block grants hand states a lump sum for a broad policy area, like community development or public health, with more flexibility. Either way, the conditions come along. The Supreme Court blessed this arrangement in South Dakota v. Dole (1987), holding that Congress may attach conditions to federal funds as long as the conditions are clearly stated, related to the federal interest in the program, and not so coercive that they stop being a real choice.6Justia Law. South Dakota v Dole, 483 US 203 (1987)
That coercion limit got its clearest test in 2012, when the Court struck down part of the Affordable Care Act’s Medicaid expansion. Congress had threatened to pull all existing Medicaid funding from any state that refused to expand. The Court held that yanking a massive, established funding stream crossed the line from encouragement to compulsion, leaving states no real choice.7Justia Law. National Federation of Independent Business v Sebelius, 567 US 519 (2012) Congress could still offer new money for expansion; it just couldn’t threaten to take away what states already had.
Mandates Without Money
Sometimes Congress imposes requirements on states without paying for them. Unfunded mandates create real friction, because states carry the compliance cost. The Unfunded Mandates Reform Act of 1995 requires federal agencies to prepare cost-benefit assessments for proposed rules that would impose $100 million or more per year on state, local, or tribal governments, and to consider less costly alternatives.8U.S. EPA. Summary of the Unfunded Mandates Reform Act The law improved transparency. It did not actually prohibit unfunded mandates, so the tension is still there.
The Commerce Clause as the Hook
The Commerce Clause gives Congress power to regulate commerce “among the several States.” Since the early twentieth century, Congress has read that authority broadly, using it to justify labor standards, environmental protection, civil rights, and consumer safety laws on the theory that these activities affect interstate commerce.1Congress.gov. Constitution Annotated – Article I Section 8 Much of the federal regulatory state hangs on that clause, and arguments over how far it reaches drive some of the sharpest fights about the scope of federal policy.
How States Drive Their Own Policy Variation
Federalism lets states try different answers to the same problem. States pioneer approaches that other states, and sometimes the federal government, later adopt. The variation this produces is significant. More than 30 states have set minimum wages above the federal floor, with rates that range widely by cost of living and political priorities. States take dramatically different approaches to healthcare access, environmental regulation, criminal sentencing, and tax structure.
The trade-off is inconsistency. A person’s rights and obligations can shift meaningfully across a state line. That variation is a feature when it tracks real differences in local needs, and it can feel arbitrary when it means access to basic services depends on geography. Federalism doesn’t resolve that tension. It bakes it into the structure of government.
Marijuana as a Live Example
Federal law still classifies marijuana as a Schedule I controlled substance with no accepted medical use. A growing majority of states have legalized medical or recreational marijuana anyway, producing a direct conflict between the two levels. The federal government has largely chosen not to enforce its prohibition against people and businesses complying with state law, and Congress has included provisions in annual appropriations bills since 2015 barring the Department of Justice from spending funds to block states from implementing their medical marijuana laws.9Congress.gov. The Federal Status of Marijuana and the Policy Gap with States
This is federalism in improvised mode. States set the operational policy, the federal government keeps its legal authority but pulls its punches, and the gap creates unresolved problems for banking, taxation, and interstate commerce. Not every federalism outcome is clean. Some are patchworks held together by informal restraint and appropriations riders.
How States Deal With Each Other
Federalism splits power vertically between Washington and the states, and it also creates a horizontal relationship among the states. Several constitutional provisions manage it.
Interstate Compacts
States enter formal agreements called interstate compacts to handle problems that cross state lines: shared water resources, regional transportation, criminal justice cooperation, professional licensing reciprocity. Article I, Section 10 says no state shall enter a compact with another state “without the Consent of Congress,” but the Supreme Court has read that pragmatically. Congressional approval is required only for compacts that would increase state power at the expense of federal authority.10Constitution Annotated. Requirement of Congressional Consent to Compacts Routine cooperative agreements between states move forward without it.
Full Faith and Credit
The Full Faith and Credit Clause in Article IV requires each state to respect the public acts, records, and court judgments of every other state.11Constitution Annotated. Overview of Full Faith and Credit Clause Win a monetary judgment in one state and the defendant moves to another, the second state’s courts must honor it. The clause stops people from shedding legal obligations by crossing a state line, and it makes the policy embedded in one state’s court rulings effective beyond that state.
Privileges and Immunities
Article IV, Section 2 entitles the citizens of each state to “all Privileges and Immunities of Citizens in the several States.” In practice, a state generally cannot discriminate against out-of-state residents when it comes to fundamental rights and economic activities. A state can charge nonresidents more for a recreational hunting license. It cannot bar them from earning a living or owning property. Even where a state does discriminate against nonresidents on a fundamental right, it must show a substantial reason and a substantial relationship between that reason and the discrimination.12Constitution Annotated. ArtIV.S2.C1.1 Overview of Privileges and Immunities Clause Together with Full Faith and Credit, this clause keeps a 50-state system from fragmenting into 50 isolated jurisdictions with no obligation to respect each other’s citizens or judgments.