How did Justice Ruth Bader Ginsburg’s opinion differ from Chief Justice Roberts’s opinion on the commerce clause?

In the 2012 Affordable Care Act cases, Chief Justice John Roberts and Justice Ruth Bader Ginsburg held fundamentally different views regarding the scope of the commerce clause.1

Chief Justice Roberts rejected the government’s argument that the individual mandate was a legitimate exercise of Congressional power under the commerce clause. He reasoned that the power to regulate commerce presupposes existing commercial activity, and he argued that the failure to purchase health insurance constitutes "inactivity" rather than activity. Consequently, he concluded that the commerce clause did not authorize Congress to compel individuals to become active in commerce by purchasing a product.12

In contrast, Justice Ginsburg, in a separate opinion joined by other justices, maintained that the individual mandate was a constitutional exercise of power under both the commerce clause and the "necessary and proper" clause. She disagreed with the distinction between commercial activity and inactivity, viewing the mandate as a valid regulation of the national health insurance market, which she argued substantially affects interstate commerce.1