The United States has a federal system. Federalism is a form of government in which power is divided between a national (federal) government and local (state) governments.

Our form of federalism is based on the U.S. Constitution. The Constitution declares that federal laws are the "supreme law of the land," after only the Constitution itself. However, the Constitution limits the federal government's powers. Governmental power is shared with the states.

The Constitution Lists the Federal Government's Powers

The federal government's powers are enumerated by the Constitution. To enumerate is to list one by one. Every law enacted by Congress must be based on one or more of these enumerated powers.

The federal government's "enumerated powers" are listed in Article I of the Constitution. They include the power to charge taxes, to create federal courts, and to declare war.

In addition, the Constitution gives the federal government certain "implied powers." While not directly stated, they are implied, or suggested, by the powers the federal government is granted. They are needed to carry out the enumerated powers. A government must be given the power to carry out its responsibilities.

The Powers Given to the States

The Constitution thus grants broad powers to the federal government. However, these powers are limited by the 10th Amendment to the Constitution. That amendment lays out the powers granted to the states. It declares that those powers not set aside for the federal government are given to the states.

As Founding Father James Madison explained, the powers given to each state "concern the lives, liberties, and properties of the people." They are needed to protect public safety and health. Such state powers are generally called "police powers."

States Can't Block Federal Laws

Finally, certain powers are called "concurrent powers." These are powers that states and the federal government both have concurrently, or at the same time. They include the power to set up courts, to charge taxes, and to spend and borrow money.

It is sometimes unclear whether the federal or state government has the power to make laws covering certain matters. As a result, two different laws dealing with the same subject can be passed. At times, these laws take opposite positions. This can lead to conflict.

The doctrine, or rule, of preemption was developed to deal with such conflicts. To preempt is to overrule. Under the doctrine, if a state law conflicts with a federal law, the state law must give way. The Constitution ensures this. It denies the states the power to block, delay or alter federal laws.

When a Federal Law Preempts a State Law

There are various situations in which federal law preempts state law. Preemption occurs when there is an obvious conflict between federal and state laws. It also occurs when it would be impossible for someone to follow both state and federal laws. Finally, it occurs when the state law undercuts federal law. In other words, a state law is preempted when it would prevent the goal of the federal law from being carried out.

The doctrine of preemption does not always apply, however. It does not apply when a federal law goes against the Constitution. In that case, the state law would win out.