The Supreme Court’s role in treaties is interpretive and constitutional, not diplomatic. The Court does not negotiate treaties or vote on them, but once a treaty is ratified it becomes part of federal law, and the justices decide what its language means, whether it and any law implementing it comply with the Constitution, and how it interacts with federal statutes and state law. That work has shaped some of the sharpest lines in American law between federal power, state authority, and individual rights.
What the Court Is Reviewing
Article II gives the President the power to negotiate treaties, but a treaty binds the United States only after the Senate approves it by a two-thirds vote of senators present and the President exchanges instruments of ratification with the other signatories.1United States Senate. About Treaties At that point the treaty carries the force of federal law and enters what the Constitution calls “the supreme Law of the Land,” alongside the Constitution itself and federal statutes.2Constitution Annotated. Supremacy Clause and the Constitutional Convention Only then does it come within the Court’s reach.
Judicial Review of Treaties and Their Implementing Laws
Because ratified treaties are supreme law, they fall within the Court’s power of judicial review. The justices can assess a treaty’s provisions and any statute Congress passes to carry it out.
The foundational case on the breadth of that power is Missouri v. Holland (1920). Missouri challenged the Migratory Bird Treaty Act of 1918, arguing that Congress had no authority to regulate wildlife within state borders. The Court disagreed, holding that the treaty power is a distinct constitutional authority and that laws needed to carry out a valid treaty are permissible even where Congress might not otherwise have power to enact them on its own.3Justia. Missouri v. Holland, 252 U.S. 416 (1920)
The Constitution Sits Above the Treaty Power
The treaty power is broad but not unlimited. In Reid v. Covert (1957), the Court held that “no agreement with a foreign nation can confer power on the Congress, or on any other branch of Government, which is free from the restraints of the Constitution.” The prohibitions of the Constitution apply to every branch and “cannot be nullified by the Executive or by the Executive and the Senate combined.”4Justia. Reid v. Covert, 354 U.S. 1 (1957) A treaty provision that collides with a First Amendment or Due Process guarantee loses. The Supremacy Clause lists treaties as supreme law; the Constitution itself sits above them.
Room for State Authority
The Court has also signaled that implementing legislation has limits when it intrudes on powers traditionally reserved to the states. In Bond v. United States (2014), the justices read a federal statute implementing the Chemical Weapons Convention narrowly to avoid applying it to a purely local poisoning. Rather than confront Missouri v. Holland head on, the Court demanded a “clear indication that Congress intended to reach purely local crimes” before letting treaty-implementing legislation override state police power.5Justia. Bond v. United States, 572 U.S. 844 (2014)
Interpreting What a Treaty Means
When a dispute about a treaty’s meaning reaches the Court, the justices decide what its terms require. They start with the ordinary meaning of the text and then look at negotiation and drafting history, including diplomatic correspondence, to understand what the signatory nations expected when they agreed to the language.
A long-standing interpretive rule shapes the way the Court reads federal statutes against this backdrop. Under the Charming Betsy canon, drawn from an 1804 opinion by Chief Justice Marshall, “an act of Congress ought never to be construed to violate the law of nations, if any other possible construction remains.”6Legal Information Institute. Murray v. The Schooner Charming Betsy The Court will read federal statutes to avoid clashing with existing treaty obligations whenever the text allows it. The rule doesn’t stop Congress from overriding a treaty, but it creates a strong presumption against accidental conflict.
Can You Actually Enforce a Treaty in Court?
Not every ratified treaty is directly enforceable in an American courtroom. The Court has drawn a line between self-executing treaties, which take effect as domestic law the moment they are ratified, and non-self-executing treaties, which create an international obligation but require implementing legislation from Congress before courts can enforce them.7Constitution Annotated. Self-Executing and Non-Self-Executing Treaties A non-self-executing treaty addresses the political branches, not the judiciary.
The Court applied that distinction sharply in Medellín v. Texas (2008). A Mexican national on death row in Texas argued that the United States had to comply with an International Court of Justice judgment ordering new hearings for Mexican nationals whose consular-notification rights had been violated. The Supreme Court held that the relevant treaties, including the UN Charter provision that member nations “undertake to comply” with ICJ decisions, were non-self-executing. That language reflected a commitment rather than a command, and without implementing legislation the ICJ judgment was not binding federal law that state courts had to follow.8Justia. Medellín v. Texas, 552 U.S. 491 (2008)
The Court went further and said the President could not unilaterally enforce the ICJ judgment either. Turning a non-self-executing treaty into domestic law is Congress’s job, not the executive’s.9Legal Information Institute. Self-Executing and Non-Self-Executing Treaties For a private litigant, this classification is decisive: it determines whether a treaty has any teeth in the courthouse.
Resolving Conflicts With Other Law
The Court regularly settles collisions between treaties and other sources of domestic law. The rules depend on what the treaty is colliding with.
Against the Constitution
The Constitution wins. Any treaty provision that conflicts with a constitutional guarantee falls, as Reid v. Covert established.4Justia. Reid v. Covert, 354 U.S. 1 (1957)
Against a Federal Statute
When a self-executing treaty clashes with a federal statute, the Court applies the later-in-time rule. As it put the point in Whitney v. Robertson (1888), “if the two are inconsistent, the one last in date will control the other, provided always the stipulation of the treaty on the subject is self-executing.”10Justia. Whitney v. Robertson, 124 U.S. 190 (1888) A treaty can supersede an earlier statute, and a later statute can override a prior treaty.11Constitution Annotated. Legal Effect of Treaties on Prior Acts of Congress The rule applies only to self-executing treaties. A non-self-executing treaty is not judicially enforceable on its own, so a federal statute prevails over it regardless of dates.
Against State Law
State law loses. Valid treaties preempt conflicting state laws under the Supremacy Clause, and the Court has enforced that principle consistently.12Constitution Annotated. Effect of Treaties on the Constitution State courts are bound by treaty obligations, and state legislatures cannot pass laws that contradict them.
Executive Agreements
Most international agreements the United States enters skip the Article II treaty process. The Court has addressed the domestic legal status of executive agreements in a line of cases that runs parallel to its treaty jurisprudence. In United States v. Belmont (1937), and again in United States v. Pink (1942), the Court recognized that the President’s foreign-affairs authority includes the power to enter binding executive agreements that override conflicting state law.
Limits emerged in Dames & Moore v. Regan (1981). The President had settled claims between U.S. nationals and the Iranian government by executive agreement as part of the hostage crisis resolution. The Court upheld the agreement, but only because Congress had historically acquiesced to presidential claims-settlement authority and had given the President broad power over foreign assets by statute. Without that congressional support, the Court indicated, the President’s actions would have been unconstitutional.13Justia. Dames and Moore v. Regan, 453 U.S. 654 (1981) Executive agreements draw their domestic legal force from congressional backing, explicit or implied, not from presidential authority alone.
Ending a Treaty
The Constitution says how treaties are made but is silent on how they end. Whether the President can terminate a treaty without Senate consent remains unresolved at the Supreme Court.
The closest the Court came was Goldwater v. Carter (1979), a challenge by several senators to President Carter’s unilateral termination of a mutual defense treaty with Taiwan. The Court vacated the lower-court decision and ordered the case dismissed but produced no majority opinion on the reasoning.14Justia. Goldwater v. Carter, 444 U.S. 996 (1979) Justice Powell’s concurrence observed that no constitutional provision “explicitly confers upon the President the power to terminate treaties,” but the practical effect of Goldwater has been to leave the President largely free to withdraw from treaties without judicial interference.15Legal Information Institute. Goldwater v. Carter, 444 U.S. 996 (1979)
What the Court Will Not Decide
Two doctrines keep certain treaty questions out of court entirely.
The Political Question Doctrine
Some decisions belong to the President and Congress alone. Under the political question doctrine, federal courts lack jurisdiction over issues the Constitution commits to the political branches or that lack “judicially discoverable and manageable standards” for resolution.16Constitution Annotated. Overview of Political Question Doctrine The Court will not weigh whether the President was wise to enter a treaty, whether the Senate should have consented, or whether the United States should recognize a particular foreign government.
Standing
Even when a treaty question is justiciable, the plaintiff must have standing. Article III requires a concrete, personal injury caused by the alleged violation. A general belief that the government is breaching a treaty is not enough. The plaintiff must show “such a personal stake in the outcome of the controversy” that participation sharpens the legal issues rather than yielding an advisory opinion.17Legal Information Institute. Standing Requirement – Overview Many treaty breaches never reach the Court for that reason. A foreign nation’s failure to honor an obligation usually produces a diplomatic dispute rather than a case an individual American can bring.