Supremacy Clause and the Supreme Law of the Land

What Is the Supremacy Clause

The clause’s full text is one sentence:

This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be 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.

It settles which law wins, not who has power in the first place. A federal law beats a state law only if Congress had the power to pass it. That is why most fights “under the Supremacy Clause” are really about something else: whether Congress acted within its powers, and whether it meant to push the state law aside.

What the Supremacy Clause Makes Supreme

The clause names three things, in this order: the Constitution, federal laws made “in Pursuance” of it, and treaties. It then tells state judges they are “bound thereby,” even when their own state’s constitution says otherwise.

Three phrases in the sentence do most of the work:

• “In Pursuance thereof.” A federal law is supreme only if it follows the Constitution. Since Marbury v. Madison in 1803, courts have struck federal laws that do not, which our judicial review explainer covers.
• “The Judges in every State shall be bound.” State courts do not get to ignore federal law. A state judge hearing a case must apply the Constitution and valid federal statutes over state law.
• “Any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.” A state cannot escape a federal rule by writing the opposite into its own constitution.

How Preemption Works Under the Supremacy Clause

The Supremacy Clause works through preemption, the rule that a valid federal law pushes aside a conflicting state law. Congress can say so outright, or the conflict can be implied from what the federal law does. Arizona v. United States lays out the implied kinds: field preemption, and conflict preemption, which covers both impossibility and obstacles.

The same word describes a different fight when a state overrides its own cities. That kind of preemption does not come from the Supremacy Clause at all, and our preemption explainer covers both, with a finder for what your state blocks your city from doing.

Courts also start from a presumption in favor of state law. In preemption cases, the Arizona Court wrote, courts should assume that “the historic police powers of the States” are not superseded “unless that was the clear and manifest purpose of Congress.” That presumption is one reason states keep winning room to go further than federal law, as with a higher minimum wage.

Landmark Supremacy Clause Rulings

The Supreme Court has spent 199 years, from McCulloch v. Maryland in 1819 to Murphy v. NCAA in 2018, marking where federal supremacy ends. McCulloch barred states from taxing a federal bank in 1819. In re Neagle shielded federal officers doing their duty in 1890. Cooper v. Aaron held states to the Court’s reading of the Constitution in 1958, 139 years after McCulloch. Printz barred Washington from ordering sheriffs around in 1997. Raich applied federal drug law inside a state that allowed marijuana in 2005. Arizona preempted a state immigration system in 2012, Armstrong said the clause alone gives no right to sue in 2015, and Murphy set the line on commandeering in 2018.

1. 1819 A state cannot tax the national bank McCulloch v. Maryland. Maryland taxed the Bank of the United States. Chief Justice Marshall, writing for the Court with no dissent, said "the power to tax involves the power to destroy," and the tax fell.
2. 1890 Federal officers doing their job are shielded from state charges In re Neagle. A deputy U.S. marshal who shot a man attacking Justice Stephen Field was freed from California murder charges because he acted under federal authority. The vote was 6-2.
3. 1958 States must obey the Supreme Court's reading of the Constitution Cooper v. Aaron. Arkansas officials could not delay integrating Little Rock Central High. All nine justices signed the opinion.
4. 1997 Washington cannot order state officers to enforce federal law Printz v. United States. The Brady Act could not require county sheriffs to run background checks. "Congress cannot circumvent that prohibition by conscripting the State's officers directly," the Court held, 5-4.
5. 2005 Federal drug law applies even where a state allows marijuana Gonzales v. Raich. Marijuana grown and used for medical purposes as California law allowed was still covered by the federal ban, 6-3.
6. 2012 States cannot run their own immigration enforcement system Arizona v. United States. Three parts of Arizona's SB 1070 were preempted by federal immigration law, 5-3. The status-check provision, section 2(B), survived for the moment.
7. 2015 The clause alone does not let you sue Armstrong v. Exceptional Child Center. The clause "instructs courts what to do when state and federal law clash," but it "certainly does not create a cause of action," the Court held, 5-4.
8. 2018 A federal law must regulate people, not order states Murphy v. NCAA. A federal ban on states authorizing sports betting fell, 6-3, because it commanded state legislatures. Justice Breyer joined that holding and dissented on how much of the law fell with it.

Sources: the Supreme Court opinions, via Cornell Legal Information Institute.

How the Supreme Court drew the lines of federal supremacy: 1819: A state cannot tax the national bank (McCulloch v. Maryland. Maryland taxed the Bank of the United States. Chief Justice Marshall, writing for the Court with no dissent, said "the power to tax involves the power to destroy," and the tax fell.). 1890: Federal officers doing their job are shielded from state charges (In re Neagle. A deputy U.S. marshal who shot a man attacking Justice Stephen Field was freed from California murder charges because he acted under federal authority. The vote was 6-2.). 1958: States must obey the Supreme Court's reading of the Constitution (Cooper v. Aaron. Arkansas officials could not delay integrating Little Rock Central High. All nine justices signed the opinion.). 1997: Washington cannot order state officers to enforce federal law (Printz v. United States. The Brady Act could not require county sheriffs to run background checks. "Congress cannot circumvent that prohibition by conscripting the State's officers directly," the Court held, 5-4.). 2005: Federal drug law applies even where a state allows marijuana (Gonzales v. Raich. Marijuana grown and used for medical purposes as California law allowed was still covered by the federal ban, 6-3.). 2012: States cannot run their own immigration enforcement system (Arizona v. United States. Three parts of Arizona's SB 1070 were preempted by federal immigration law, 5-3. The status-check provision, section 2(B), survived for the moment.). 2015: The clause alone does not let you sue (Armstrong v. Exceptional Child Center. The clause "instructs courts what to do when state and federal law clash," but it "certainly does not create a cause of action," the Court held, 5-4.). 2018: A federal law must regulate people, not order states (Murphy v. NCAA. A federal ban on states authorizing sports betting fell, 6-3, because it commanded state legislatures. Justice Breyer joined that holding and dissented on how much of the law fell with it.).

1819: Maryland taxed notes issued by the Second Bank of the United States. In McCulloch v. Maryland, Chief Justice John Marshall wrote for the Court, with no dissent, that “the power to tax involves the power to destroy,” and that a state cannot use it against the national government.

1890: Deputy U.S. Marshal David Neagle shot and killed David Terry, who attacked Justice Stephen Field at a train-station restaurant in Lathrop, California, in 1889. In In re Neagle, the Court held 6-2 that California could not try him for murder: he was doing what federal law authorized, and if he “did no more than what was necessary and proper for him to do, he cannot be guilty of a crime under the law of the state of California.” That ruling is the root of what lawyers now call Supremacy Clause immunity.

1958: Arkansas officials sought to delay integrating Little Rock Central High. In Cooper v. Aaron, signed by all nine justices on September 29, 1958, the Court wrote: “No state legislator or executive or judicial officer can war against the Constitution without violating his undertaking to support it.”

1997: The Brady Act told county sheriffs to run gun buyers’ background checks. In Printz v. United States, the Court held 5-4 that Washington cannot command state officers to carry out a federal program: “Congress cannot circumvent that prohibition by conscripting the State’s officers directly.”

2005: Angel Raich and Diane Monson used marijuana for medical purposes, as California law allowed. Monson grew her own, and caregivers supplied Raich’s. In Gonzales v. Raich, the Court held 6-3 that the federal drug ban still applied to them.

2012: In Arizona v. United States, the Court held 5-3 that three parts of Arizona’s SB 1070 were preempted by federal immigration law, including a state crime for failing to carry federal registration papers. Justice Elena Kagan took no part.

2015: In Armstrong v. Exceptional Child Center, the Court held 5-4 that the Supremacy Clause “instructs courts what to do when state and federal law clash” but “certainly does not create a cause of action” for a private party to enforce a federal law.

2018: A federal law barred states from authorizing sports betting. In Murphy v. NCAA, the Court struck it 6-3, because it ordered state legislatures what not to pass instead of regulating people directly. “Congress can regulate sports gambling directly, but if it elects not to do so, each State is free to act on its own,” Justice Samuel Alito wrote.

When State and Federal Law Collide

Most real conflicts land in one of two places: federal law wins outright, or the state keeps room because Washington cannot order it to help. The table sorts common collisions by which law wins and why.

The pattern answers a common confusion. The Supremacy Clause lets federal law override a state’s rules, but it does not turn state officials into federal employees. Our sanctuary cities explainer covers how that line plays out in immigration, and our federalism explainer covers how the two levels share power.

Supremacy Clause Fights in 2025 and 2026

The live fights are about immigration enforcement and climate lawsuits. States are testing how far they can regulate or prosecute federal agents working inside their borders. The Supreme Court heard argument on October 5, 2026 on whether federal law bars state climate suits against oil companies.

Where the Supremacy Clause fights stand

As of October 15, 2026

• California ban on masked officers (SB 627) Blocked by a court, mask ban on hold for federal agents

  A federal judge put the mask ban on hold for federal agents on February 9, 2026, finding it discriminated against the federal government, and no party appealed. SB 1004, which adds state officers to meet that ruling, was signed September 29, 2026. (source)

• California ID requirement for federal agents (SB 805) Blocked by a court, for federal officers

  The district court declined to block it in February 2026. The Ninth Circuit blocked it pending appeal on April 22, 2026, finding it "attempts to directly regulate the United States in its performance of governmental functions," and on October 14 ordered the district court to enter a preliminary injunction. (source)

• Minnesota assault charges against ICE agent Christian Castro In litigation, next hearing Nov. 3

  Hennepin County announced four counts of second-degree assault and one of falsely reporting a crime on May 18, 2026. Castro first appeared in state court on September 17, and his next appearance is set for November 3. A federal grand jury separately indicted him in September for lying about the shooting, Reason reported. (source)

• Suncor v. Boulder County (climate lawsuit preemption) In litigation, argued Oct. 5

  The Supreme Court heard argument on October 5, 2026 on whether federal law precludes Boulder's state-law climate claims against oil companies, and on whether it has jurisdiction to hear the case. Justice Alito is not participating. (source)

• Missouri law declaring federal gun laws void (SAPA) Final ruling, struck down

  A federal judge struck the 2021 law, and the Eighth Circuit affirmed on August 26, 2024: "a State cannot invalidate federal law to itself." (source)

Source: Supreme Court docket; Sen. Scott Wiener; Office of the Governor of California; Ninth Circuit opinions; Hennepin County Attorney; Reason; Eighth Circuit opinion

The agent cases turn on the test from Neagle: was the agent doing something federal law authorized, and was it “necessary and proper” to the job? Vice President J.D. Vance has said a federal officer engaged in federal law enforcement has “absolute immunity” from state prosecution. Reason’s Jacob Sullum answered that the defense applies only when an officer “reasonably” believed he was acting within his federal authority, and that a federal judge would decide that before trial if the case is moved to federal court. Our 4th Amendment explainer covers the force and search rules those cases measure against.

The Honest Disagreement Over Federal Supremacy

Claims of state power against Washington have come from every direction. In 1956 Arkansas amended its constitution to oppose the Supreme Court’s desegregation decisions, and Cooper v. Aaron rejected that resistance. Missouri defended its 2021 gun law under Printz. In 2025 and 2026, Illinois, New York and Colorado won dismissal of Justice Department suits over their sanctuary laws.

A few distinctions keep the argument honest:

• Supremacy is not a blank check. Federal law wins only when Congress acted within its powers. Printz and Murphy show the Court striking federal laws that reached too far.
• Nullification is not the same as refusing to help. A state cannot declare a federal law void. Virginia’s 1798 resolutions claimed a right to “interpose,” Kentucky’s 1799 resolutions called nullification “the rightful remedy,” South Carolina declared federal tariffs “null, void, and no law” in 1832, and Missouri tried in 2021. A state can refuse to lend its own officers, which the anti-commandeering rule protects.
• Preemption cuts both ways. Federal supremacy ended Arkansas’s resistance to desegregation in Cooper. It has also displaced state injury law: in Riegel v. Medtronic (2008), the Court ruled 8-1 that federal device law barred New York claims over a catheter the FDA had approved.
• Immunity for federal officers has limits. Neagle protects officers doing their authorized duty. Courts decide case by case where that duty ends.

What You Can Do

1. Know which level wins before you act. If your state allows something federal law bans, such as marijuana, the federal ban still applies to you, as Raich held.
2. Follow the Suncor climate case. The Supreme Court heard it on October 5, and its docket posts the briefs and the argument transcript. Unless the Court finds it lacks jurisdiction, the ruling will decide whether cities and states can sue oil companies over climate change under their own laws.
3. Ask Congress, not only your state, about federal agents. Courts have blocked states from setting rules for federal agents that they do not apply to their own officers, and from regulating the United States directly. A rule that binds every federal agent in every state has to come from Congress. Use our guide to writing your representative to ask yours.
4. Study the citizenship test answer with someone preparing for it. The USCIS civics questions are free, and helping a neighbor study is one of the most direct ways to support new citizens.