
The relationship between federal and state laws in the United States is a complex one, with the potential for conflict and disagreement. While the federal government may want states to adopt certain laws, it does not happen automatically, and the federal government is limited in how it can make states comply. Federal law is enforced through a combination of public and private efforts, with many federal statutes authorizing civil enforcement by federal agencies and the states. State enforcement of federal law is a unique model of enforcement and a unique form of state power, with states acting on behalf of interests that may differ from those of federal enforcers. The Supremacy Clause of the US Constitution addresses possible conflicts between state and federal laws, with the doctrine of preemption stating that federal law supersedes state law in many but not all cases. While states can declare federal laws unconstitutional, this has no legal effect unless the courts agree.
| Characteristics | Values |
|---|---|
| Federal law enforcement | Public and private efforts |
| Who has the authority to enforce federal law? | Federal agencies and states, typically through their attorneys general |
| State enforcement | Decentralized |
| Can federal law enforcement be refused by states? | Yes, but federal law supersedes state law in many (but not all) cases of conflicting laws |
| Can federal law enforcement be refused by state officials? | Yes, if the state has determined the federal law to be unconstitutional |
| Can states impede federal authorities from enforcing their own law if the state deems the law to be unconstitutional? | No |
| Can states nullify federal laws? | Yes, but not all |
| Can the federal government use the military to enforce federal laws? | Yes, but it is rare and has historically been reserved for emergencies |
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What You'll Learn

Federal law enforcement by state authorities
Federal laws are enforced through a combination of public and private efforts. Most federal civil statutes vest enforcement authority in a federal agency, and some also allow private parties to sue to enforce federal law.
State enforcement of federal law is a unique model of enforcement and a unique form of state power. State enforcement is largely decentralized, and states act on behalf of a set of interests that differ significantly from those of federal enforcers. While state officials are not required to enforce federal laws that the state has determined to be unconstitutional, states may not block federal authorities from enforcing a federal law unless a court has ruled that the law is unconstitutional.
In the 1997 case, Printz v. United States, the Supreme Court ruled that the federal government could not mandate state law enforcement authorities to conduct background checks. Similarly, in New York v. U.S., the Supreme Court held that a federal law requiring states to regulate the disposal of radioactive waste according to Congress' instructions was outside Congress' powers and inconsistent with the Tenth Amendment.
The National Guard, under the control of state governors, can be activated within a state for purposes authorized by state laws and regulations. When activated, their conduct, including the use of force, is governed by state law. However, the Posse Comitatus Act prohibits the National Guard from carrying out civilian law enforcement functions. In rare cases, the President can invoke the Insurrection Act and deploy federal troops to enforce federal laws if civilian agencies and courts are not functioning, as in the case of Brown v. Board, where President Eisenhower deployed troops to protect the Little Rock Nine from a violent mob.
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State sovereignty and refusal to enforce federal regulations
The US Constitution's Supremacy Clause addresses the conflict between state and federal laws. The Supremacy Clause includes the doctrine of "preemption," which states that federal law takes precedence over state law in the event of a conflict in most cases. However, federal authorities are not prevented from enforcing their own laws by state regulatory activity, and state workers are not directly involved in activities like cultivation or sales but rather administer licenses for private companies.
The Supreme Court has held that Congress cannot directly compel states to enact and enforce a federal regulatory program. In cases such as Hodel v. Virginia Surface Mining & Reclamation Assn., Inc., the Court upheld the Surface Mining Control and Reclamation Act of 1977 because it did not "commandeer" states into regulating mining. The Court found that states were not required to enforce steep-slope standards, expand state funds, or participate in the federal regulatory program. Similarly, in FERC v. Mississippi, the Court observed that it had never explicitly sanctioned a federal command to states to promulgate and enforce laws and regulations.
In Printz v. United States, the Supreme Court held that a federal law requiring state officials to conduct background checks as part of a federal program violated constitutional principles of state sovereignty. The Brady Act, which established a five-day federal waiting period for handgun purchases and mandated background checks, was found to be unconstitutional. The Court reaffirmed this principle in New York v. United States, holding that the federal government could not enact a regulatory program that "commandeers" state legislative and administrative mechanisms to enforce federal law.
State enforcement of federal law is a unique model of enforcement and state power. While enforcement authority typically follows from regulatory authority, state enforcement of federal law breaks this link by authorizing state actors to enforce the laws of a different sovereign. State enforcement is decentralized, and states act on behalf of interests that may differ significantly from those of federal enforcers. This enables states to adjust the intensity of enforcement and interpret federal law in their own way.
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Supremacy Clause and preemption of state laws
The US Constitution's Article VI.4, also known as the Supremacy Clause, addresses the potential conflict between state and federal laws. The Supremacy Clause includes the preemption doctrine, which states that federal law supersedes state law in most cases of conflicting laws. This doctrine gives the federal government broad powers to create, regulate, and enforce laws.
The Supremacy Clause establishes federal law as the "supreme law of the land," mandating that judges in every state adhere to the federal government's Constitution, laws, and treaties in matters under its control. Federal law prevails over state law in the event of a conflict, and states must meet or exceed the federal standard. This hierarchy applies only when the two laws contradict each other, requiring one to be disregarded.
The preemption doctrine can be express or implied. Express preemption occurs when a federal statute or regulation explicitly conflicts with state law, while implied preemption refers to situations where federal law interferes with or contradicts state law. Conflict preemption applies in areas such as drug manufacturing, administration, and labeling, where federal regulatory schemes may override state court decisions.
While the Supremacy Clause gives the federal government significant authority, there are limits to its power. The Tenth Amendment, for example, protects states from federal overreach, as seen in New York v. U.S. (1992), where the Supreme Court ruled that a federal law requiring states to regulate radioactive waste disposal exceeded Congress's enumerated powers and violated state sovereignty.
Additionally, the federal government's ability to enforce its laws in states is influenced by federalism, where enforcement authority enables states to adjust enforcement intensity and interpret federal laws. State enforcement of federal laws empowers different state representatives, such as attorneys general, who may act independently from the state legislature and governor. This dynamic can lead to unique state enforcement models and influence state power.
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Nullification of federal laws by states
Nullification is a constitutional theory that asserts that individual states can invalidate federal laws or judicial decisions deemed unconstitutional. This theory has been controversial since its inception in early American history. Between 1798 and the beginning of the Civil War in 1861, several states threatened or attempted nullification of various federal laws. However, none of these efforts were legally upheld, and the Supreme Court rejected nullification attempts in a series of 19th-century decisions. The Civil War ended most nullification efforts, and in the 1950s, the Supreme Court again rejected nullification attempts by southern states, explicitly holding that states may not nullify federal law.
The legitimacy of nullification as a constitutional theory has been rejected in American history. The Constitution does not contain any clause expressly providing that states have the power to declare federal laws unconstitutional. The federal courts, including the Supreme Court, have consistently held that under the Constitution, states do not have the power to nullify federal laws. They have rejected the "compact theory," finding that the Constitution was not a contract among the states, but rather established directly by the people. Under the Supremacy Clause of Article VI, the Constitution and federal laws made in pursuance thereof are "the supreme law of the land," superseding state laws and prohibiting negation by states.
Despite the rejection of nullification by the federal courts, supporters of nullification argue that the states' power of nullification is inherent in the nature of the federal system. They contend that before the Constitution was ratified, the states were essentially separate nations. In their view, the Constitution is a contract or "compact" among the states, through which they delegated certain powers to the federal government while retaining all other powers for themselves. According to this interpretation, the states have the inherent right to judge compliance with the compact and declare federal laws unconstitutional if they determine that the federal government has exceeded its delegated powers.
Nullification has played a significant role in shaping American history, with three prominent attempts by states at nullification. Firstly, in 1798, Kentucky's attempt to nullify the Alien and Sedition Acts, which were passed during the Quasi-War with France and outraged Thomas Jefferson, John Adams's vice president. Jefferson anonymously drafted the Kentucky Resolutions, declaring the acts unconstitutional and "altogether void and of no force" in Kentucky. Secondly, in 1832, South Carolina's attempt to nullify two federal tariff laws, the Tariff of 1828 and the Tariff of 1832, which they believed disproportionately burdened southern states. This led to the Nullification Crisis, with Vice President John C. Calhoun justifying South Carolina's Ordinance of Nullification by following Jefferson's argument that states could "veto" federal acts they deemed exceeded the federal government's powers. Thirdly, in 1957, Arkansas's attempt to nullify Brown v. Board of Education, a landmark case on racial segregation in schools.
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Deployment of military troops to enforce federal laws
The Posse Comitatus Act, enacted in 1878, generally prohibits the federal government from using the military as a domestic police force to enforce federal laws. The Act bars federal troops from participating in civilian law enforcement unless expressly authorized by law. However, there are exceptions and loopholes to this Act.
Firstly, the Insurrection Act allows the President to deploy the military to enforce federal laws, suppress rebellions, or protect civil rights in a state, with or without the state government's consent. The Insurrection Act gives significant power to the President to decide when and where to deploy the military, and its broad language has been criticised for its lack of clarity and definition.
Secondly, the Posse Comitatus Act does not apply to the National Guard, which can participate in law enforcement if it aligns with state law. When National Guard personnel are federalised, they become subject to the Posse Comitatus Act until they are returned to state control.
Thirdly, the Department of Defense has claimed that the Constitution grants military commanders emergency authority to use federal troops to address large-scale civil disturbances or protect federal property when local governments cannot or will not.
Fourthly, there is ambiguity regarding the use of troops in advisory, support, disaster response, or homeland defence roles, as opposed to explicit domestic law enforcement. For example, in 2009, soldiers from Fort Rucker were deployed to Alabama in response to a shooting spree to assist in traffic control and crime scene security.
Fifthly, there are specific circumstances where the military may be used to enforce federal laws. For instance, the military may assist in responding to terrorist bombings and providing surveillance and intelligence for drug interdiction and counter-terrorism missions.
Finally, the Enforcement Acts allowed the President to deploy the military when state authorities were unable or unwilling to suppress violence that violated citizens' constitutional rights.
In conclusion, while the Posse Comitatus Act generally prohibits the use of the military in domestic law enforcement, several exceptions and loopholes exist that enable the federal government to deploy troops to enforce federal laws in certain situations.
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Frequently asked questions
The federal government can enforce state laws through a combination of public and private efforts. Federal civil statutes vest enforcement authority in a federal agency, and some also allow private parties to sue to enforce federal law. State enforcement is decentralized, and states act on behalf of interests that differ from those of federal enforcers.
Yes, states can refuse to enforce federal laws that they deem to be unconstitutional. In the 1997 case *Printz v. United States*, the Supreme Court ruled that the federal government could not compel state law enforcement authorities to conduct background checks. However, states may not obstruct federal authorities from enforcing a federal law unless a court has ruled the law unconstitutional.
The domestic deployment of the military is rare and has been reserved for emergencies, such as war, armed rebellion, or to enforce federal laws when civilian agencies and courts are not functioning. An example is the 1958 deployment of federal troops to Arkansas by President Eisenhower to enforce the Supreme Court's decision in *Brown v. Board of Education*.











































