Andrew Koppelman is correct that Hammer v. Dagenhart would be the most obvious precedent for a Supreme Court decision striking down the ACA:
Both then and now, challengers to the statutes had to propose that the Supreme Court invent new constitutional rules in order to strike them down. At the time it considered the issue in 1918, there was nothing in the Supreme Court’s case law that suggested any limit on Congress’s authority over what crossed state lines. On the contrary, the Court had upheld bans on interstate transportation of lottery tickets, contaminated food and drugs, prostitutes, and alcoholic beverages.
That’s why the Supreme Court’s invalidation of the law in 1918 astounded even those who had most strenuously opposed enactment. Hammer v. Dagenhart declared—in tones reminiscent of the Broccoli Objection to Obamacare—that if it upheld the law “all freedom of commerce will be at an end, and the power of the States over local matters may be eliminated, and, thus, our system of government be practically destroyed.” Justice Oliver Wendell Holmes, dissenting, wondered how it could make sense for congressional regulation to be “permissible as against strong drink but not as against the product of ruined lives.” The Court responded that unlike all the contraband that it had permitted Congress to block, the products of child labor “are of themselves harmless.” This meant a completely novel constitutional doctrine: The Court took unto itself the power to decide which harms Congress was permitted to consider when it regulated commerce.
What the Court actually accomplished in 1918 was to thwart democracy and consign large numbers of children to the textile mills for more than two decades. Health care is another context in which the fear of federal power creates a serious risk of ravaging the lives of large numbers of actual people. If the law is upheld, no one is going to be forced to buy broccoli. But if the law is struck down, large numbers of people will die of preventable or treatable diseases, or be bankrupted by medical expenses.
Of course, some Tea Partiers are indeed proud to say that the shoe made with child labor fits.
Another key reason the analogy works is that Hammer was really a “liberty of contract” case in disguise, like arguments against the ACA. The Supreme Court’s inconsistent application of commerce clause restrictions during this area made it clear that they objected to the ends, not the means, of the bans on shipping goods made with child labor. If they approved of the ends, the use of federal power was fine. In both cases, “state sovereignty” is not the real animating issue.