Cambridge, Mass.

THE new mandate to buy health insurance has now reached the Supreme Court, which agreed on Monday to judge its constitutionality. The crux of the constitutional complaint against the mandate is that Congress’s ability to regulate commerce has never been understood to give it the power to force Americans to buy insurance, or anything else.

But not only is there a precedent for this, there is also clear support for it in the Constitution. For decades, Americans have been subject to a mandate to buy a health insurance plan — Medicare. Check your paystub, and you will see where your contributions have been deducted, whether or not you wanted Medicare health insurance.

Many opponents dismiss this argument because Medicare (unlike the new mandate) requires the purchase of health insurance as a condition of entering into a voluntary commercial relationship, namely employment, which Congress can regulate under the commerce clause. Thus, they say, the Medicare requirement regulates a commercial activity, whereas the new mandate regulates inactivity. But is that a distinction of substance? After all, we don’t have much choice but to get a job if we want to eat.

Even if you accept this distinction, it means that Congress can mandate the purchase of health insurance as long as it conditions that mandate on engagement in some commercial activity. So the challengers would have to admit that a statute saying that “anyone who has ever engaged in commercial activity must buy health insurance” would be constitutional. This is effectively the same as the mandate, because it is hard to believe that anyone in this nation has never bought or sold anything in his life.