In his opinion today in United States v. Comstock, Justice Breyer gives us a textbook example of how the Supreme Court, over the years, has converted the Constitution into modern “constitutional law,” which is connected to the Constitution only occasionally. This is policy trumping law, pure and simple.

The question before the Court was whether Congress had the power, under the Constitution, to commit mentally ill, sexually dangerous prisoners beyond the date they would otherwise be released. The problem, as Breyer grants, is that Congress has only certain enumerated powers, and the only power it has to criminalize conduct, beyond the three crimes mentioned in the Constitution, is pursuant to one of those enumerated powers — in particular, through the last of its 18 enumerated powers, its power to enact laws that are “necessary and proper” for “carrying into execution” one of the previous 17 enumerated powers or ends. In other words, Congress can criminalize conduct only if doing so is necessary and proper for carrying out one of its other constitutionally authorized powers.

Under its power to regulate interstate commerce, however, Congress has criminalized all manner of conduct not remotely related to insuring a free national market, the main function of the commerce power. The conduct criminalized here is the possession of child pornography. That’s a responsibility that belongs to the states, under state police power, not to the federal government. And that’s where today’s problem began.

But Breyer has compounded it by holding that even though the Constitution nowhere grants Congress the power to criminalize the conduct in question, Congress can invoke its instrumental power under the Necessary and Proper Clause to commit these prisoners beyond the date they would otherwise be released. In other words, he has turned an instrumental power, dependent on Congress’s other powers, into an independent power. That’s how government expands beyond the limits imposed by the Constitution.