The federal courts are sometimes asked to decide whether a federal health, safety, or environmental standard preempts a stricter standard adopted by one or more states. The practical stakes for advocates of environmental and consumer protection in these cases have been high in recent years, in no small part because the executive branch and Congress have been either hostile to, or ambivalent to the point of inaction with respect to, proposals for federal standards that would impose significant costs on business. From a broader normative vantage, how the federal courts respond to preemption challenges affects how vibrant a role the states can have in democratic governance, and thus affects how vibrant a role the people-"We the People"-can have in democratic governance. Preemption is an issue that implicates not just particular regulatory outcomes, but also our fundamental commitments to preserving and fostering democratic values.
The recent wave of state laws regarding greenhouse gas emissions poses exactly the question whether a lax federal standard serves as a regulatory cap or as a floor.1 The most populous state-California-has adopted rules that would in effect require carmakers to market more fuel efficient cars than are required under the federal fuel economy statute and regulations.2 Twelve other states have followed suit, and more may join them.3 California and the states that have adopted the California rules account for a very sizeable percentage of the nation's population. California argues that its rules are fully consistent with the policies, objectives, and text of the federal Clean Air Act.4 The automobile industry argues that federal law, in particular the fuel economy standards provisions of the Energy Policy and Conservation Act (EPCA), preempts the California rules.5 The federal agency responsible for promulgating federal fuel economy standards, the National Highway and Traffic Safety Administration (NHTSA), has issued what might be termed an interpretive rule that tracks the automobile industry position.6 The environmental, economic, and political importance of this controversy is almost impossible to overstate because stronger California rules (coupled with stronger rules in other states) could lead ultimately to more fuel efficient cars throughout the United States and perhaps even outside the United States. Three separate district courts are now hearing the question of preemption of state greenhouse gas emissions rules for automobiles, and we may well observe a flurry of opinions before the controversy finally winds its way up to the Supreme Court.7
Federal preemption doctrine is, famously, a mess, replete with poorly defined, overlapping, hyperformalistic categories.8 Express preemption provisions in federal statutes are relatively few, and when present, they often contain highly ambiguous terms.9 Many preemption cases, even some that the courts nominally treat as express preemption cases, involve a judicial inquiry as to whether Congress implicitly preempted a particular state law or program. Within the rubric of implied preemption, the courts rely heavily on various categories-field preemption, conflict or obstacle preemption, and foreign affairs preemption-that lack defined borders, that blur together in specific cases, and that sometimes seem to do little analytic work.10
One ostensibly uncontroversial proposition in preemption doctrine is that congressional intent governs whether, and to what extent, federal law preempts state law." The practical problem, of course, is that implied preemption inquiries ask the federal courts to answer a wholly hypothetical question: if Congress had spoken directly and unambiguously to the precise preemption question at hand, which it did not, what would it have said? The courts have materials available to them to guide this inquiry, including congressional statements of statutory purposes, the structure and language of the statutes, legislative history, and federal agency regulations. …