In its decision today upholding the constitutionality of the Affordable Care Act, the Supreme Court, by a five-to-four vote, held that the individual mandate provision (requiring uninsured individuals who can afford to buy health insurance to do so) was justified by the Congress' power to tax, but not by its power to regulate interstate commerce. In the end, the difference may seem insignificant. When all the dust settled, the individual mandate is constitutional. But it is nonetheless worth understanding the disagreement about the reach of the Commerce Clause, because this was the primary focus of most of the public debate leading up to the decision and was also the subject of the wildly popular broccoli hypothetical.

Only one justice thought the Act was constitutional under the taxing power but not the commerce power -- Chief Justice Roberts. The other eight justices thought the Act was either constitutional (Ginsburg, Breyer, Sotomayor, Kagan) or unconstitutional (Scalia, Kennedy, Thomas, Alito) under both provisions.

To understand why Ginsburg, Breyer, Sotomayor and Kagan were right about the constitutionality of the Act under the Commerce Clause (even though they lost five-to-four on that issue), I have reprinted below a heavily-edited and abridged (by me) excerpt from Justice Ginsburg's dissenting opinion on the Commerce Clause issue. In my view, it absolutely shreds the opposing view and, in any event, is an excellent primer on the question:

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