IN UNITED STATES V. CAROLENE PRODUCTS (1938), the Supreme Court considered the constitutionality of a federal statute that prohibited interstate shipments of “filled milk” – skimmed milk compounded with nonmilk fats, such as vegetable oil. Although government lawyers maintained that filled milk might contain threats to human health, the supporting evidence was flimsy. The real purpose of the statute was almost certainly to protect the dairy industry, which possessed considerable political clout at the time, against unwanted competition from a cheaper substitute. Yet the Supreme Court resoundingly upheld the statute. Less than a year after the demise of the Lochner regime, judicial deference to legislative judgments was the order of the day. The bitter lessons taught by Lochner's collapse had sunk in.

But what exactly were those lessons? Was aggressive judicial review to protect individual liberties to be rejected across the board? Earlier chapters in this book have shown that the answer was no. In the years following its Carolene Products decision, the Court quickly developed a new agenda, foreshadowed by a remarkable footnote in that case that Supreme Court Justice Lewis F. Powell once called “the most celebrated footnote in constitutional law.” In that footnote, the Court explained that, although it had largely abandoned review of economic legislation for fairness or reasonableness under the Due Process Clause, it would not defer to Congress and the state legislatures with respect to all matters. Most famously, the Court said that statutes “directed at particular religious, or national, or racial minorities” might continue to warrant exacting judicial review – a development later reflected in some of the Court's most lauded decisions under the Equal Protection Clause, including Brown v. Board of Education (1954), which forbade race discrimination in the public schools.