Two constitutional provisions at issue in the health-care challenges are the “necessary and proper” clause and the commerce clause.

Necessary and proper clause: Congress has the power to “make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States, or in any department or officer thereof.”

Commerce clause: Congress has the power “to regulate commerce with foreign nations, and among the several states, and with the Indian tribes.”

McCulloch v. Maryland, 1819

Chief Justice John Marshall wrote the landmark opinion, which turned aside Maryland’s challenge of Congress’s power to establish the Second Bank of the United States. He cited the necessary and proper clause, which the court said allows Congress to pass laws to create a functioning national government, even if the power is not specifically listed in the Constitution.

Wickard v. Filburn, 1942

The court said Congress’s power under the commerce clause allows it to regulate activities that have even an indirect effect on interstate commerce. That meant that the Agricultural Adjustment Act applied even to Ohio farmer Roscoe Filburn, who was growing wheat for use on his own farm.

United States v. Lopez, 1995

For the first time since the New Deal, the court said that Congress exceeded its power under the commerce clause. By a 5 to 4 vote, the court struck down the Gun-Free School Zones Act, saying that regulating the carrying of handguns was too far removed from “commerce” to be justified under the commerce clause.

Among the current justices, Antonin Scalia, Anthony M. Kennedy and Clarence Thomas were in the majority; Justices Ruth Bader Ginsburg and Stephen G. Breyer dissented.

United States v. Morrison, 2000

The court said Congress had used the commerce clause to justify a law that did not touch economic activities, and it struck parts of the Violence Against Women Act. It said the law, which gave victims of gender-related attacks the right to sue in federal court, was too far removed from the subject of the commerce clause.

Scalia, Kennedy and Thomas were in the majority; Ginsburg and Breyer dissented.

Gonzales v. Raich, 2005

The court reversed its trend, holding that the commerce clause gives Congress the right to criminalize the production and use of homegrown marijuana, even when states have approved its cultivation and use. The court said an inability to regulate such marijuana would undermine the federal Controlled Substances Act and relied on Wickard in its decision.

Kennedy, Ginsburg and Breyer were in the majority; Scalia filed a concurring opinion; Thomas dissented.