United States v. Gilmore was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The case arose when the petitioner, John Gilmore, was arrested by federal officers in the state of California and taken into federal custody. Gilmore then filed a petition for a writ of habeas corpus in the state court, seeking to be released from federal custody. The federal government argued that the state court did not have the authority to issue the writ, as the federal government had exclusive jurisdiction over the matter. The Supreme Court ultimately held that the state court did not have the authority to issue the writ of habeas corpus. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's exclusive jurisdiction over the matter. The Court also noted that the writ of habeas corpus was a fundamental right, and that the federal government had the power to protect that right. In conclusion, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's exclusive jurisdiction over the matter.

In United States v. Gilmore, the Supreme Court was asked to decide whether a federal court had jurisdiction over a case involving an alleged violation of state law. The majority opinion held that the federal court did not have jurisdiction in this instance because it involved only matters of state law and no issues of national importance or constitutional questions were present. Justice Field dissented from this decision, arguing that Congress had given the federal courts authority to hear cases arising under any laws made by them pursuant to their enumerated powers in Article I, Section 8 of the Constitution. He argued further that since Congress has power over interstate commerce and other areas affecting citizens throughout the country, they should be able to use their judicial branch as well as its legislative one for enforcement purposes when necessary. Furthermore, he noted that if such cases are left solely up to state courts then there is potential for unequal justice depending on which states' laws are being applied; thus allowing federal courts access would ensure uniformity across all states regardless of local statutes or customs.