The Supreme Court takes federalism seriously. In a series of 5-4 decisions, the current Court has been the first post-New Deal court to attempt to ensure that the federal government does not exceed its enumerated powers or unduly intrude upon state authority. Chief Justice Rehnquist and Justices O’Connor, Scalia, Kennedy and Thomas have, over biting dissents from the Court’s four liberals, restricted Congress’s authority in ways that were previously unimaginable....