Thomas Sowell examines this week the dangerous lengths to which courts have extended the reach of the Constitution’s Commerce Clause.

Over the years, “interstate commerce” became magic words to justify almost any expansion of the federal government’s power, in defiance of the Tenth Amendment. That is what the Obama administration is depending on to get today’s Supreme Court to uphold its power to tell people that they have to buy the particular health insurance specified by the federal government.

There was consternation in 1995 when the Supreme Court ruled that carrying a gun near a school was not interstate commerce. That conclusion might seem like only common sense to most people, but it was a close 5 to 4 decision, and it sparked outrage when the phrase “interstate commerce” failed to work its magic in justifying an expansion of the federal government’s power.

The 1995 case involved a federal law forbidding anyone from carrying a gun near a school. The states all had the right to pass such laws, and most did, but the issue was whether the federal government could pass such a law under its power to regulate interstate commerce.

The underlying argument was similar to that in the 1942 case of Wickard v. Filburn: School violence can affect education, which can affect productivity, which can affect interstate commerce.

Since virtually everything affects virtually everything else, however remotely, “interstate commerce” can justify virtually any expansion of government power, by this kind of sophistry.

The principle that the legal authority to regulate X implies the authority to regulate anything that can affect X is a huge and dangerous leap of logic, in a world where all sorts of things have some effect on all sorts of other things.