The Constitution divides power among three branches but rarely draws precise boundaries. Over two centuries, the Supreme Court has filled in the details in disputes between Congress and the President, between the branches and agencies, and over its own role. These cases determine who can make, enforce, and interpret the law.
This guide groups the landmark cases by theme and explains what each decided and why it still matters.
Chevron v. NRDC in 1984 told courts to defer to reasonable agency interpretations of ambiguous laws, but Loper Bright Enterprises v. Raimondo overruled it in 2024. In West Virginia v. EPA in 2022, the Court formalized the major questions doctrine, requiring clear authorization from Congress for agency actions of vast economic or political significance. In Learning Resources v. Trump on February 20, 2026, the Court held that an emergency powers law did not authorize sweeping tariffs, with three justices relying on the major questions doctrine.
In INS v. Chadha in 1983, the Court struck down the legislative veto, by which one house of Congress could overturn executive actions, holding that Congress must act through bicameral passage and presentment to the President. In Clinton v. City of New York in 1998, it struck down the line item veto because only Congress can amend or repeal a law. In NLRB v. Noel Canning in 2014, the Court held that the Senate is in session when it says it is, limiting recess appointments during short breaks.
In Marbury v. Madison in 1803, Chief Justice John Marshall held that a provision of the Judiciary Act of 1789 was unconstitutional and that it is emphatically the province and duty of the judicial department to say what the law is. The Court used the power sparingly for decades. In Cooper v. Aaron in 1958, rejecting Arkansas officials' resistance to school desegregation, the Court declared that its interpretations of the Constitution bind state officials. Baker v. Carr in 1962 narrowed the political question doctrine, opening apportionment disputes to the courts.
In Myers v. United States in 1926, the Court upheld the President's power to fire executive officers. Humphrey's Executor v. United States in 1935 allowed Congress to protect independent commissioners from removal, and Morrison v. Olson in 1988 upheld the independent counsel. Later decisions moved back toward presidential control, from Free Enterprise Fund in 2010 to Seila Law v. CFPB in 2020. On June 29, 2026, Trump v. Slaughter overruled Humphrey's Executor, while Trump v. Cook treated the Federal Reserve as a special case.
The Court has also defined limits on judicial power. Standing doctrine requires a concrete injury, and the political question doctrine leaves some disputes to the elected branches, as in Rucho v. Common Cause in 2019 on partisan gerrymandering. In Trump v. CASA in 2025, the Court held that federal courts generally cannot issue universal injunctions. Supporters of the Court's recent direction say it restores the Constitution's structure and accountability, while critics say it has expanded presidential power and its own while weakening Congress and agencies.
When President Truman seized steel mills during the Korean War, the Court ruled against him in Youngstown Sheet and Tube Co. v. Sawyer in 1952. Justice Robert Jackson's concurrence set out three categories: presidential power is strongest when backed by Congress, uncertain when Congress is silent, and weakest when the President acts against Congress's will. In United States v. Nixon in 1974, the Court unanimously rejected an absolute executive privilege over evidence needed for a criminal trial, and in Trump v. United States in 2024 it recognized broad immunity for a former President's official acts.
See the principle behind these cases in checks and balances in action, explore agency power in independent agencies vs. departments, or learn the methods judges use in judicial philosophies explained.