Read: What happens to Obamacare now?

The constitutional challenges to Obamacare harken back to the first great debate over the powers of Congress. In 1791, then–Treasury Secretary Alexander Hamilton proposed establishing a national bank to act as financier to the federal government. Congressional opponents objected that the Constitution gave no express power to create a national bank. Supporters responded that Congress necessarily possessed implied powers to effectuate those specifically enumerated in the Constitution.

Late in the debate, Congressman James Madison offered a novel constitutional theory against the bank bill. Yes, there were implied powers, he conceded, but those could reach only minor matters and could not extend to “great, substantive, and independent” objects, no matter how useful to implementing the enumerated powers. Creating a national bank fell into this latter “great powers” category.

Madison’s argument was voted down by a two-thirds House majority. Congress passed the bank bill, and President George Washington signed it into law.

This victory for implied congressional powers was confirmed by the Supreme Court three decades later, when states’ rights advocates challenged the constitutionality of the Second Bank of the United States, chartered by Congress to succeed Hamilton’s bank in 1816—at the request of President James Madison. In the celebrated 1819 case of McCulloch v. Maryland, Marshall upheld the constitutionality of the second bank. Although the Constitution did not expressly authorize Congress to create banks, Marshall concluded that under the Necessary and Proper Clause, Congress may enact any legislation that is “conducive,” “convenient,” “useful,” or “plainly adapted” to implementing an enumerated power.

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To take a modern example: Nothing in the Constitution expressly authorizes Congress to impose a military draft. But because that is a reasonable means to implement the express power “to raise and support armies,” military conscription has been recognized as an implied power.

In the 2012 Obamacare decision, Roberts could have joined the four liberals to uphold the individual mandate under the Commerce Clause power “to regulate commerce … among the several states.” Individuals who choose not to purchase health insurance may or may not be engaged in interstate commerce. But if an individual mandate to purchase health insurance is useful for effective regulation of the interstate health-care market, Congress has the implied power to enact it, according to Marshall’s theory in McCulloch.

Instead, Roberts joined the four conservative justices to define “commerce” as “economic activity,” and to conclude that the Commerce Clause does not permit Congress to regulate the “inactivity” of someone’s refusal to buy health insurance. Relying on Madison’s 1791 House speech, Roberts argued that regulating the “inactivity” of refusing to buy health insurance is “a great, substantive, and independent power” that cannot be implied, no matter how effective it might be in regulating the national health-care market.