The United States is a constitution-based federal system, meaning power is distributed between a national (federal) government and local (state) governments.

Although the Supremacy Clause states that the Constitution, federal laws, and treaties are the “supreme law of the land,” according to the Supreme Court, it is clear that the Constitution created a federal government of limited powers. The Supreme Court has noted that “every law enacted by Congress must be based on one or more of its powers enumerated in the Constitution.”

These limited powers are set forth as what are termed “enumerated powers” in Article I, Section 8 of the Constitution. These enumerated powers include, among other things, the power to levy taxes, regulate commerce, establish a uniform law of naturalization, establish federal courts (subordinate to the Supreme Court), establish and maintain a military, and declare war.

In addition, the Necessary and Proper Clause has been interpreted by the Supreme Court to define “implied powers,” those which are necessary to carry out those powers enumerated in the Constitution. In McCulloch v. Maryland, Justice John Marshall set forth the doctrine of implied powers, stating, that a government entrusted with great powers must also be entrusted with the power to execute them.

While the Constitution thus grants broad powers to the federal government, they are limited by the 10th Amendment, which states that “[t]he powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

As James Madison explained, “[t]he powers reserved to the several States will extend to all the objects which, in the ordinary course of affairs, concern the lives, liberties, and properties of the people, and the internal order, improvement, and prosperity of the State.”

These reserved powers have generally been referred to as “police powers,” such as those required for public safety, health, and welfare.

Finally, certain powers are called concurrent powers, which the states and the federal government both may exercise. These can include, for example, setting up courts, levying taxes, and spending and borrowing money. Typically, these are powers necessary for maintenance of public facilities.

As can be appreciated, one of the difficulties in the federal system is determining which entity, if any, has the power to legislate in a particular realm. In general, the problem of conflicting laws between the states and the federal government has given rise to what is called the doctrine of preemption.

Under this doctrine, based on the Supremacy Clause, if a state or local law conflicts with a federal law, the state or local law must give way (unless the federal law is itself unconstitutional, in other words, it exceeds the power of the federal government). As Justice Marshall put it in McCulloch v. Maryland, “[s]tates have no power, by taxation or otherwise, to retard, impede, burden, or in any manner control the operations of the Constitutional laws enacted by Congress to carry into execution the powers vested in the Federal Government.”

Under this doctrine, the Supreme Court has indicated that the Supremacy Clause may entail preemption of state law either by express provision, by implication, or by a conflict between federal and state law. If there is an express provision in the legislation, or if there is an explicit conflict between the state law at issue and the federal law, the state law provision is immediately invalid. Field preemption occurs when Congress legislates in a way that is comprehensive to an entire field of an issue. Impossibility preemption occurs when it would be impossible for someone to comply with both state and federal laws. Purposes and objectives preemption occurs when the purposes and objectives of the federal law would be thwarted by the state law.