Last week, the U.S. Supreme Court ruled that the feds can constitutionally prohibit the personal cultivation and use of marijuana for medicinal purposes.  Rightly regarded as a setback for medical-marijuana supporters, the decision is just as significant for what it says about federal power.

Two California women were using homegrown cannabis to treat pain and nausea, as prescribed by their physicians and in accordance with state law.  Gonzales (formerly Ashcroft) v. Raich essentially held that the interstate commerce clause -- the enumerated congressional power to “regulate Commerce… among the several states” -- allows Congress to ban this practice, even though it involves noncommercial activity taking place entirely within the boundaries of a single state.  The activity in this case was smoking pot, but the logic of the decision could just as easily be extended to church suppers and local flea markets.

As Justice Clarence Thomas wrote in his dissent:  “Respondents Diane Monson and Angel Raich use marijuana that has never been bought or sold, that has never crossed state lines, and that has had no demonstrable effect on the national market for marijuana. If Congress can regulate this under the Commerce Clause, then it can regulate virtually anything -- and the Federal Government is no longer one of limited and enumerated powers.”

Yet six out of nine justices -- including one of the Court’s most outspoken conservatives -- agreed that something does not have to be “interstate” or “commerce” in order to be regulated under the interstate commerce clause.  All that is needed is a semi-plausible argument that a broader national regulatory scheme would be undermined by leaving the activity untouched and, presto, out goes federalism.

The commerce clause wasn’t always interpreted as a catch-all escape hatch to justify regulation in areas where the federal government lacked explicit constitutional authority.  The Constitution was amended to abolish slavery and ban the sale or manufacture of alcoholic beverages.  Congress didn’t think to take either action based on the commerce clause, even though both activities affected interstate commerce far more substantially than many things so regulated today.

In fact, as syndicated columnist Jacob Sullum has pointed out, when Congress originally passed the Marihuana Tax Act of 1937 it tried to control the drug through a complicated tax and regulatory system rather than an outright ban under the commerce clause.  This is presumably because members of Congress did not believe the clause gave them such power.

The purpose of the Constitution was to create a limited federal government with few defined powers.  It was not supposed to be an exhaustive list of the people’s rights, but of Washington’s lawful claims.  But today we have a highly centralized government, often justified by court decisions that invoke a Constitution the Framers, the ratifying public and generations of Americans across the political spectrum would not recognize.

We are no longer surprised when that Constitution fails to act as an effective brake on the federal government.  As far back as 1942, in Wickard v. Filburn, the Supreme Court ruled that Washington may prevent a farmer from growing wheat for his own personal consumption on the grounds it may affect national price-control measures.  Important checks and balances have been falling away for years, threatening to take the whole concept of limited government with them.

Raich therefore is nothing new.  But to believers in limited constitutional government, it should serve as a useful reminder.  Liberals and conservatives alike are often willing to discard constitutional restraints on federal authority to protect their preferred policy outcomes.  And libertarians -- such as Randy Barnett, who argued Raich before the Supreme Court last November -- counting on judges to be the first line of defense in enforcing the Constitution may wish to reconsider their position.

Whatever your view of the marijuana policy the Supreme Court upheld in Raich, all of us benefit from jurisprudence that takes seriously a Constitution of limited government, not loopholes.

W. James Antle III is a primary columnist for Intellectual Conservative.com.  He works as an assistant editor of The American Conservative magazine and is also a senior editor of EnterStageRight.com. The views expressed here represent his alone.