The Supremacy Clause
Why the Supremacy Clause Is Suddenly Controversial Again
For most of American history, the Supremacy Clause sat quietly in the background—quietly understood, entirely unglamorous, and largely uncontested. It was structural plumbing. You didn’t argue about it unless something had already gone wrong. That quiet has ended.
Today, state–federal conflict has returned with force, most visibly in immigration policy, border security, and enforcement priorities. States pass laws to counter federal inaction. Other states enact policies designed to outright obstruct federal enforcement. Lawsuits follow. Injunctions pile up. Governors and attorneys general invoke “sovereignty” while federal agencies invoke “preemption.” The result is not mere clarity, but constitutional fog.
What’s driving the conflict is not a mystery. When federal law is enforced unevenly—or not at all—states feel pressure to act. But when states act independently in areas reserved to the national government, the constitutional order itself is strained. The question is no longer academic: Can a republic function when federal law is no longer supreme in practice, even if it remains supreme on paper?
The Supremacy Clause was written precisely to prevent this kind of fragmentation. It exists to stop selective compliance, regional defiance, and legal patchworks that weaken the Union from within. Understanding why it was written—and how it is meant to operate—is essential if we want to distinguish legitimate federalism from slow-motion nullification.
The Text of the Supremacy Clause
The Supremacy Clause is found in Article VI, Clause 2 of the Constitution, and its language is both direct and deliberate. It declares that “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.” It then adds a critical enforcement mechanism: “the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.”
Every phrase matters. Supremacy is not granted to anything labeled “federal,” but only to the Constitution itself and to laws made in pursuance of it. That qualifier is doing real work. It makes clear that unconstitutional federal acts are not supreme, and that supremacy is tied to lawful authority, not to mere power.
Just as important is who is bound. The Clause does not merely instruct citizens or legislators. It explicitly binds state judges, even when state constitutions or statutes point in the opposite direction. The Framers anticipated resistance at the state level and closed the loophole in advance. When federal and state law conflict, judges are not free to choose which they prefer. The hierarchy is fixed.
The Supremacy Clause is therefore not a grant of unlimited federal power. It is a rule of decision. It tells courts what to do when two valid sovereigns collide. Without it, the Constitution would be aspirational rather than operative—dependent on voluntary compliance rather than on legal obligation.
The Problem the Framers Were Solving
The Supremacy Clause was not born out of abstract theory. It was a direct response to failure—specifically, the failure of the Articles of Confederation. Under the Articles, the national government could pass resolutions and enter treaties, but it lacked any effective mechanism to ensure that states complied. Federal authority existed in name, not in practice.
States routinely ignored congressional directives, refused funding for national obligations, and violated international agreements. Some imposed tariffs on their neighbors. Others openly defied treaties with foreign powers, exposing the young nation to diplomatic retaliation and to economic chaos. Congress could request compliance, but it could not compel it. The result was fragmentation, weakness, and disunion.
The Framers understood that a government whose laws could be nullified by local preference was not a government at all. It was a suggestion box. Without supremacy, every federal act became optional, and national policy dissolved into regional vetoes. The Union could not defend itself, regulate commerce, or speak abroad with one voice.
The Supremacy Clause was designed to end this dynamic decisively. It ensured that once federal law was validly enacted, it would bind the states, whether or not they approved. not a rejection of federalism, but a preservation of it. A system of divided sovereignty requires a clear rule for resolving conflict. Without supremacy, the Constitution would have recreated the same impotence that nearly destroyed the republic in its infancy.
How the Clause Was Defended at the Founding
At the Founding, the Supremacy Clause was not controversial because it expanded federal power, but because it clarified how a federal system could function at all. Its defenders understood that without a clear hierarchy of law, the Constitution would collapse under the same pressures that ruined the Articles of Confederation. Supremacy was not a theory of domination. It was a rule of coherence.
In Federalist No. 33, Alexander Hamilton addressed the concern head-on. Laws made pursuant to the Constitution, he argued, must be supreme by definition. To deny this was to deny the possibility of law itself. A government whose acts could be overridden by subordinate authorities was not sovereign in any meaningful sense. Supremacy, in Hamilton’s view, was not an aggressive claim—it was a logical necessity.
James Madison reinforced this point in Federalist No. 44. He warned that allowing states to disregard federal law would invite the very abuses the Constitution was designed to prevent: instability, factionalism, and mutual hostility—all among the states. Madison emphasized that supremacy applied only to laws made within constitutional bounds, preserving the balance between national authority and state sovereignty.
Critically, the Framers rejected the idea of state nullification at the outset. The Constitution did not envision states as final arbiters of federal law. That role belonged to the courts. Supremacy was paired with judicial review to ensure that disputes were resolved through law rather than defiance. In this way, the Clause was defended not as a threat to liberty, but as a safeguard for it.—ensuring that constitutional government could actually govern.
Supremacy vs. Federalism: Clearing the Confusion
Much of the modern confusion surrounding the Supremacy Clause comes from a basic category error: treating supremacy as a claim of unlimited federal power rather than a rule for resolving legal conflict. The Clause does not erase federalism. It makes federalism workable.
Supremacy does not mean that the federal government may act wherever it wishes. It means that when the federal government acts within its constitutional authority, its laws take precedence over conflicting state law. The distinction is critical. The Clause assumes limits on federal power; it does not abolish them. That is why the text carefully restricts supremacy to laws made “in pursuance” of the Constitution.
Federalism still governs vast areas of American life. States retain broad police powers over health, safety, property, education, and local governance. They legislate freely where Congress has not acted and may even regulate in parallel where Congress has acted, unless federal law preempts them. Supremacy does not swallow state authority; it disciplines conflict.
The Tenth Amendment reinforces this balance by reserving powers not delegated to the federal government to the states and the people. But a reservation is not a veto. States do not have the power to nullify federal law simply by asserting sovereignty. Federalism divides power vertically when necessary; supremacy orders it when those divisions collide.
In other words, supremacy answers a narrow question that is nonetheless unavoidable: what happens when two valid sovereigns issue contradictory commands? Without an answer, the system breaks down. With it, national unity and state autonomy can coexist.
Treating the Supremacy Clause as an enemy of federalism misunderstands its purpose. It is not a weapon against the states. It is the rule that keeps fifty governments from becoming fifty competing nations.
The Doctrine of Preemption
The Supremacy Clause does not operate in the abstract. Its practical effect is carried out through the doctrine of preemption—the legal mechanism courts use to determine when state law must give way to federal law. Preemption is not an invention of activist judges. It is the unavoidable consequence of a constitutional system in which federal law is supreme when validly enacted.
Preemption takes several forms. The most straightforward is express preemption, where Congress explicitly states in a statute that federal law overrides state regulation in a particular area. When Congress speaks clearly, the analysis is simple: states may not legislate in ways the statute forbids.
More complex—and more common—is implied preemption. This comes in two varieties. Field preemption occurs when federal regulation is so comprehensive that courts conclude Congress intended to occupy the entire field, leaving no room for state law. Conflict preemption when state law makes compliance with federal law impossible or stands as an obstacle to the objectives Congress sought to achieve.
What matters is not motive, but effect. A state law may be well-intentioned, popular, or otherwise rooted in legitimate local concerns. If it interferes with federal objectives in an area where Congress has authority, it must yield. Preemption is not a judgment about the wisdom of state policy. It is a rule about constitutional hierarchy.
This is why preemption is unavoidable in any functioning federal system. Without it, national laws would fracture into fifty variations, enforcement would become optional, and policy would become impossible to make uniform. Preemption is how the Supremacy Clause moves from principle to practice—ensuring that when Congress lawfully acts, the law actually governs.
Immigration as a Core Federal Power
Immigration has long been understood as a core federal responsibility, not because the Constitution uses the modern word “immigration,” but because the powers implicated—sovereignty, foreign relations, national security, and naturalization—are inherently national in character. Decisions about who may enter the country, what conditions they must meet, and what legal status they will have. They cannot be coherently managed by fifty separate governments acting independently.
From the earliest days of the republic, the federal government asserted primary authority over questions of entry, exclusion, and removal. Control over borders is inseparable from the power to conduct foreign affairs, regulate commerce with other nations, and define membership in the political community. A patchwork of state immigration regimes would invite diplomatic conflict, inconsistent enforcement, and competing definitions—all of which would be national policy—precisely the problems the Constitution was written to avoid.
Uniformity is the key principle. Immigration law cannot mean one thing in Arizona, another thing in Texas, and yet another thing in California without ceasing to function as law at all. A nation must be able to speak with one voice about who is permitted to enter, to remain, or to be removed. That necessity is not ideological; it is structural.
This does not mean states have no role. States may cooperate with federal authorities, assist in federal enforcement, and regulate within their traditional police powers where federal law allows. But cooperation is not the same as control. States may not create parallel immigration systems, redefine federal categories, or impose their own enforcement priorities in ways that conflict with national law.
Immigration sits at the intersection of internal order and external sovereignty. For that reason, it has always fallen within the heartland of federal power—and when state action intrudes into that space, the Supremacy Clause is not an intrusion. It is the constitutional boundary doing its job.
States, Immigration, and the Limits of Independent Action
The tension between federal supremacy and state frustration is most visible in immigration because it is an area where federal failure—or perceived failure—produces immediate local consequences. States bear the costs of unlawful entry in education, healthcare, housing, and law enforcement, yet lack ultimate authority over admission, removal, or status. That pressure tempts states to act independently. The Constitution draws a firm line between what is understandable and what is permissible.
States are not powerless. They may cooperate with federal immigration enforcement, share information, honor lawful detainers where permitted, and regulate conduct within their traditional police powers so long as those laws do not conflict with federal objectives. States may also decline to assist federal enforcement under the anti-commandeering doctrine. What they may not do is create a parallel immigration regime that competes with federal law, contradicts it, or obstructs it.
This distinction—cooperation versus independent regulation—is where many disputes arise. When a state attempts to define immigration crimes differently, impose state penalties that alter federal priorities, or condition state policy on immigration status in forbidden ways, it crosses from assistance into interference. Intent does not save such laws. Even well-motivated state action can be unconstitutional if it frustrates federal design.
Conversely, when states adopt policies that deliberately impede federal enforcement—by prohibiting information sharing, blocking detainee access, or imposing cooperation penalties—the constitutional analysis turns on obstruction rather than supremacy. The federal government cannot compel state enforcement, but states cannot actively undermine federal law either. Neutral non-cooperation is permitted; obstruction is not.
The Supremacy Clause exists precisely to police this boundary. It does not require states to fix federal policy failures. It requires them not to replace national law with local substitutes. In a constitutional system, dissatisfaction with enforcement does not authorize defiance of authority.
Supreme Court Case Law: The Last Twenty Years
Over the past two decades, the Supreme Court has repeatedly been asked to clarify how the Supremacy Clause operates in practice—especially in the context of immigration. The Court’s decisions have been consistent on one core point: immigration enforcement is primarily a federal responsibility, while state laws that intrude into that domain are subject to preemption.
The most direct statement came in Arizona v. United States. Arizona had enacted a sweeping immigration law intended to supplement what state officials viewed as federal inaction. While the Court allowed limited cooperation provisions to stand, but it struck down several core sections. The reasoning was decisive: Congress had occupied the field of immigration enforcement, and state efforts to create parallel crimes, penalties, or enforcement schemes conflicted with federal objectives. Even where state goals aligned with federal policy in theory, the Constitution did not permit states to pursue them independently.
A year earlier, the Court addressed a narrower question in Chamber of Commerce v. Whiting. There, the Court upheld an Arizona law revoking business licenses from employers who knowingly hired unauthorized workers. The key distinction was congressional intent. Federal law expressly preserved a limited role for states in licensing, and Arizona’s law operated within that carve-out. The case illustrates that supremacy does not erase state authority—it turns on what Congress has authorized.
In United States v. Texas, the Court confronted federal enforcement discretion rather than state power. Although the case ended in a procedural stalemate, it underscored a critical principle: decisions about immigration priorities rest with the federal executive (subject to congressional limits)—not with the states.
Finally, Murphy v. NCAA clarified a frequent source of confusion. The federal government may not compel states to enforce federal law, and anti-commandeering does not weaken supremacy. Federal law still preempts conflicting state law; states simply cannot be required to enforce it.
Taken together, these cases draw a clear constitutional map. States may assist federal efforts. They may regulate where Congress allows. They may decline to participate. But they may not redefine, obstruct, or replace federal immigration law. When they try, the Supremacy Clause—not ideology—decides the outcome.
Sanctuary Policies and Supremacy Clause Tensions
Sanctuary policies sit at the most misunderstood intersection of the Supremacy Clause and modern federalism. Much of the public debate collapses important legal distinctions into slogans—either claiming that sanctuary policies are flatly unconstitutional or insisting that they are immune from any constitutional scrutiny. Neither claim is correct.
At their core, most sanctuary policies are not affirmative violations of the Supremacy Clause. Under the anti-commandeering doctrine, the federal government cannot require states or localities to use their own resources to enforce federal law. A state may decline to participate in immigration enforcement, just as it may decline to assist in enforcing other federal regulatory schemes. Neutral non-cooperation, by itself, is constitutionally permissible.
But neutrality has limits. Sanctuary policies begin to raise Supremacy Clause concerns when they cross from refusal into obstruction. A state or locality may choose not to help, but it may not actively interfere with federal enforcement. Laws or ordinances that prohibit information sharing with federal authorities, restrict access to detainees, or penalize state employees for cooperating with federal agents can move from passive non-assistance into affirmative resistance.
This distinction matters because the Supremacy Clause does not merely prevent states from contradicting federal law on paper. It also prevents them from undermining federal objectives in practice. A policy designed to frustrate enforcement rather than simply abstain from participation risks preemption of conflict even if it avoids explicit contradiction.
Much of the political rhetoric surrounding sanctuary jurisdictions obscures this nuance. The Constitution does not require states to act as immigration officers, nor does it permit them to create legal safe zones that impede federal authority. The line is narrow, technical, and often litigated—but it is real.
Sanctuary policies are therefore not categorically lawful or unlawful. Their constitutionality turns on design, effect, and intent. The Supremacy Clause does not demand state cooperation but demands that state policy not become a tool for nullification by another name.
Border Security and Federal Enforcement Authority
Border security sits at the core of federal sovereignty. Control over national borders is not simply an administrative function or a policy preference; it is one of the defining attributes of a nation-state. Decisions about who may enter the country, under what conditions they may do so, and how the law is enforced at the border implicate foreign relations, national defense, and the integrity of citizenship itself. For that reason, border enforcement has always been understood as an exclusively federal responsibility.
State frustration in this area is understandable. Border states bear disproportionate costs when federal enforcement falters, and the consequences are immediate rather than merely abstract. But constitutional authority does not shift simply because enforcement is perceived as inadequate. The Supremacy Clause does not contain an exception for federal neglect. States do not acquire independent authority to redefine border policy when they disagree with federal priorities.
This is the hard constitutional reality: enforcement failure does not dissolve supremacy. A state may assist federal border operations if invited or authorized. It may use its police powers to address secondary effects—crime, trespass, trafficking—so long as those efforts do not function as de facto immigration enforcement. What it may not do is assume control over admission, removal, or immigration policy by unilateral action.
The danger is not merely legal. When states attempt to fill perceived federal vacuums with independent enforcement regimes, the result is fragmentation. Border policy becomes inconsistent, enforcement becomes unpredictable, and signals to foreign actors become mixed about American law. That undermines deterrence, diplomacy, and legitimacy—all at once.
The Supremacy Clause exists to prevent precisely this outcome. A nation that allows its border policy to devolve into fifty competing strategies ceases to act as a nation. Federal authority over border security is not optional and is not conditional. It is a structural requirement of constitutional order.
The Real Risk: Soft Nullification
The most serious threat to the Supremacy Clause today is not open defiance, but something quieter and more corrosive: soft nullification. Unlike the blunt nullification theories of the 19th century, modern resistance rarely announces itself as such. It operates through simple delay, selective enforcement, administrative resistance, and endless litigation. Federal law remains “supreme” in theory while being hollowed out in practice.
Soft nullification thrives in complexity. Agencies reinterpret statutes to avoid enforcement. States pass laws carefully drafted to evade direct conflict while still frustrating federal objectives. Courts are asked to referee not whether federal law exists, but whether it can function at all. The result is a legal environment where supremacy is acknowledged rhetorically but denied operationally.
This form of nullification is especially dangerous because it avoids accountability. No one claims to be rejecting federal authority outright. Instead, responsibility is diffused across bureaucracies, courts, and jurisdictions. Enforcement slows. Compliance becomes optional. The law remains on the books, but its effect depends on national geography, partisan politics, and administrative will.
History offers a warning here. The Framers were not only concerned about dramatic acts of rebellion. They feared gradual erosion—states complying when convenient and resisting when costly. That is why the Supremacy Clause binds judges directly and does not rely on goodwill alone. A constitutional system cannot survive on selective obedience.
When federal law becomes something to be negotiated rather than to be applied, the rule of law itself degrades. Citizens no longer know which rules govern them. States begin to behave less like members of a union and more like rival power centers. Soft nullification does not announce a constitutional crisis. It creates one by attrition.
The Supremacy Clause was written to prevent this slow unraveling. Ignoring it does not produce healthy decentralization. It produces legal fragmentation—and, eventually, political fracture.
What the Supremacy Clause Preserves
The Supremacy Clause is not merely a technical provision for resolving disputes between statutes. It preserves the basic conditions under which a constitutional republic can function at all. At its core, it ensures national coherence—the ability of the United States to act as a single legal and political entity rather than a loose collection of competing jurisdictions.
Without supremacy, the equal application of law collapses. Citizens would be subject to different federal rules depending on where they live, not because Congress intended variation, but because states would choose compliance selectively. Law would cease to be a stable guide to conduct and would become a moving target shaped by local politics. Supremacy preserves predictability, which is essential not only for governance but also for liberty itself.
The Clause also protects federalism by preventing it from degenerating into fragmentation. A true federation requires both divided authority and a mechanism for resolving conflict between those divisions. Supremacy provides that mechanism. It allows states wide latitude within their proper sphere while ensuring that national decisions—once lawfully made—are actually operative. Without it, federalism becomes a veto system in which no collective action is reliable.
Just as importantly, the Supremacy Clause preserves legitimacy. A government that cannot enforce its own laws loses credibility with its citizens and coherence with foreign entities. Allies, adversaries, and markets all respond to whether national commitments are real or contingent. Supremacy ensures that when the United States speaks through law, it speaks with authority.
In short, the Clause draws the line between a nation and an alliance. It preserves unity without abolishing diversity, authority without embracing absolutism, and law without permitting negotiation. Without supremacy, the Constitution becomes aspirational. With it, the republic becomes governable.
Supremacy as a Condition of Survival
The Supremacy Clause is not an ideological preference or a partisan weapon. It is a structural necessity. The Framers understood that a nation incapable of enforcing its own laws is not merely inefficient—it is unstable. Supremacy was written to ensure that constitutional government could actually govern, that national decisions could not dissolve into regional defiance, and that the Union could be more than a voluntary association held together by convenience.
This does not mean federal power is unlimited, nor does it excuse federal failure. Poor enforcement, bad policy, or executive abdication are political problems to be corrected through elections, legislation, and lawful challenge. But they do not nullify constitutional authority. The answer to federal dysfunction is reform, not fragmentation. Once states begin substituting their own judgments for national law, the rule of law itself becomes conditional.
History is unambiguous on this point. Republics do not usually fall all at once. They erode when law becomes negotiable, when enforcement becomes geography-dependent, and when authority becomes optional. The Supremacy Clause exists to halt that erosion and to draw a hard line beneath constitutional order, saying: this law applies everywhere, or it applies nowhere.
A nation that cannot enforce its borders, its statutes, or its constitutional hierarchy cannot long remain a nation. Supremacy is not about centralization for its own sake. It is about coherence, legitimacy, and survival. If the Constitution is to remain more than a statement of values—if it is to remain binding law—then the Supremacy Clause must be understood, respected, and enforced.