Developed doctrine under the Supremacy Clause can be divided into two closely related categories. Within the first category are those cases in which there exists a potential conflict between federal and state law. In such cases, if a conflict is established, the federal law is said to preempt—i.e., to supplant—the state law. Under these circumstances, the state law is void, just as it would be if it conflicted with a provision of the Constitution. This was the type of problem presented in Gibbons. State and federal statutes regarding licensing for the coastal trade conflicted and, as a consequence, the federal law preempted the state law.
The second doctrinal category involves those cases in which a state attempts to tax or regulate the federal government or an instrumentality of the federal government. Again, if the state law disrupts a federal program, the state law must give way to federal law. In essence, the federal government and its instrumentalities are immune from such state-imposed interference. Thus in McCulloch, the Second Bank of the United States was immune from Maryland’s attempt to impose a tax on it.
One should be able to see the close relationship between these two doctrinal categories. Indeed, in describing McCulloch, one could just as easily say that the federal law chartering the bank “preempted” the state’s effort to tax the bank. So, too, one could describe the federal licensee in Gibbons as immune from the restrictions of state law. In fact, as we discuss further below, the doctrine of immunity is really nothing more than a specialized type of preemption in which the “preemptive” conflict takes the form of a tax or regulation directed at the activities of the federal government. Whether a potential conflict is characterized as triggering preemption or immunity, however, the result is the same: If a true conflict exists, state law must yield to the superior federal authority.
In the sections that follow, we examine both categories of federal supremacy. Keep in mind that an underlying presumption of each is that the federal law must itself be valid under appropriate constitutional standards. If the federal law is not valid, the Supremacy Clause is of no effect. Thus a conflict between a state law and the Gun-Free School Zones Act—the law struck down in United States v. Lopez, 514 U.S. 549 (1995), as beyond the commerce power (see §5.3.4)—would not trigger the Supremacy Clause. In essence, a conflict with an unconstitutional federal law is no conflict at all.
The final section of this chapter examines the related problem of state-imposed term limits on federal elective office.
The preemption doctrine mandates that valid federal law, including statutes, treaties, executive agreements, administrative rules, and common law, supplants or supersedes state law that is inconsistent with the specific terms or overall objectives of the federal law. See El Al Israel Airlines, Ltd. v. Tseng, 525 U.S. 155 (1999) (preemptive effect of treaty); Fidelity Federal Sav. & Loan Assn. v. De La Cuesta, 458 U.S. 141, 153-154 (1982) (preemptive effect of federal regulations).