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The Supremacy Clause makes clear that the Constitution, federal laws, federal regulations, and treaties take superiority over similar state laws. The clause allowed the Supreme Court to help establish a strong federal government. The Supremacy Clause was included in the U.S. Constitution because the Articles of Confederation lacked such a clause. Under the Articles, federal laws did not and could not supersede state laws. In the Federalist Papers, James Madison defended the need for the Supremacy Clause, noting that state legislatures held all powers not specifically given to the federal government by Article I and Article II. Therefore, he argued, the Supremacy Clause was needed to balance the scales of government.
In McCulloch v. Maryland, Chief Justice John Marshall solidified the Supremacy Clause as the ultimate authority in United States constitutional law. That decision set out a standard for the entire judiciary; when state laws and the Constitution are in conflict, the Constitution wins.
Article VI, Clause 3 of the United States Constitution:
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.
United States Library of Congress, The Constitution of the United States of America: Analysis and Interpretation
The Supremacy Clause was a response to problems with the Articles of Confederation (the Articles), which governed the United States from 1781 to 1789. The Articles conspicuously lacked any similar provision declaring federal law to be superior to state law. As a result, during the Confederation era, federal statutes did not bind state courts in the absence of state legislation implementing them. To address this issue and related political difficulties, the Confederation Congress called for a convention in 1787 to revise the Articles. While the Supremacy Clause was not a source of major disagreement at the Constitutional Convention that followed, it generated intense controversy during debates over the Constitution's ratification. But advocates of federal supremacy prevailed. The Constitution was ratified in 1788 with the Supremacy Clause.
The Supremacy Clause is among the Constitution's most significant structural provisions. In the late 18th and early 19th centuries, the Supreme Court relied on the Clause to establish a robust role for the federal government in managing the nation's affairs. In its early cases, the Court invoked the Clause to conclude that federal treaties and statutes superseded inconsistent state laws. These decisions enabled the young republic to enforce the treaty ending the Revolutionary War, charter a central bank, and enact other legislation without interference from recalcitrant states.1
The Supreme Court continued to apply this foundational principle—that federal law prevailed over conflicting state law—throughout the latter half of the 19th century.2 But other aspects of the Court's federalism jurisprudence limited the Supremacy Clause's role during that era. Throughout this period, the Court embraced what academics have called the doctrine of "dual federalism," under which the federal government and the states occupied largely distinct, non-overlapping zones of constitutional authority.3 While federal supremacy persisted as a background principle during these years, the Court's bifurcation of federal and state authority minimized the instances in which the two could conflict.4
To the extent that the Supremacy Clause did play an explicit role in the federalism disputes of this era, the Supreme Court applied it in ways that reinforced dual federalism's sharp division of federal and state power. In a series of early-20th-century decisions, the Court developed a precursor to the doctrine of "field preemption"—the principle that some federal legislation implicitly prevents states from adopting any laws regulating the same general subject. Some of the Court's early field preemption decisions aggressively employed the new doctrine, concluding that any congressional action in certain fields automatically displaced all state laws in those fields.5
But the Supreme Court's initial foray into field preemption soon gave way to broader legal and political trends. During the New Deal era of the 1930s and 1940s, the Court acceded to demands for a more active national government by revising other elements of its federalism jurisprudence.6 This about-face marked the demise of dual federalism, as the Court expanded the areas in which the federal government and the states possessed concurrent authority. To prevent the federal government's newly expanded powers from smothering state regulatory authority, the Court simultaneously narrowed the circumstances in which federal law displaced state law. Besides retreating from the "automatic" field preemption of the early 20th century, the Court articulated a "presumption against preemption," under which federal law does not displace state law "unless that was the clear and manifest purpose of Congress."7
As the above discussion suggests, the Supreme Court has channeled contemporary Supremacy Clause doctrine into the language of "federal preemption." The Court's cases recognize several types of preemption. At the highest level of generality, federal law can preempt state law either expressly or impliedly. Federal law expressly preempts state law when it contains explicit language to that effect.8 By contrast, federal law impliedly preempts state law when that intent is implicit in its structure and purpose.9
The Court has also identified different subcategories of implied preemption. As noted, field preemption occurs where federal law is "so pervasive as to make reasonable the inference that Congress left no room for the States to supplement it," or where "the federal interest is so dominant that the federal system will be assumed to preclude enforcement of state laws on the same subject."10 In contrast, conflict preemption occurs where compliance with both federal and state law is impossible ("impossibility preemption") or where state law poses an obstacle to federal objectives ("obstacle preemption").11
Because preemption issues are primarily questions of statutory interpretation, the Supremacy Clause's role in contemporary legal doctrine differs from that of many other constitutional provisions. The basic principle enshrined in the Clause—federal supremacy—is now well-settled. Generally, litigants do not dispute the Clause's meaning or advance conflicting theories on its scope. Rather, preemption cases ordinarily turn on the same types of issues—like the textualist/purposivist divide and administrative deference—that recur in all manner of statutory litigation.12
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