Kaine involved a British extradition request, under the terms of a treaty with the United States, for a suspect wanted for assault with intent to murder in Ireland. Thomas Kaine was arrested on a warrant issued by a U.S. commissioner (the forerunner of the U.S. magistrate judge) after a request by the British consul in New York. After Kaine sued for a writ of habeas corpus, a U.S. district judge sitting on a U.S. circuit court found his detention to be legal and remanded him into custody. The secretary of state then ordered that he be turned over to the British authorities. Kaine next sought a writ of habeas corpus from Justice Nelson, the circuit justice for the Second Circuit, which included New York.

Believing the case presented important issues, Nelson adjourned it to the next term of the Supreme Court so that it could be heard by all the justices. The Court determined, however, that it could not exercise original jurisdiction over a habeas corpus petition. Anticipating this ruling, Kaine’s counsel filed another habeas corpus petition directly in the Supreme Court accompanied by a petition for a writ of certiorari to have the circuit court decision brought up for review. The Court refused to release Kaine, with four justices denying the writ on the merits and another for lack of jurisdiction. Three justices, including Nelson, dissented from the ruling.

The Supreme Court not having acted on the habeas corpus petition originally presented to him, Nelson proceeded to decide the case while sitting on the circuit court. He discharged Kaine from custody, finding that the commissioner had lacked jurisdiction to order his arrest in the first place. Because extradition requests could potentially involve “political offenses,” Nelson believed that it was improper for the courts to act until a foreign government had made a formal request of the executive branch and the president of the United States had issued a mandate for the suspect’s extradition. “It is a general principle,” he wrote, “as it respects political questions concerning foreign governments, that the judiciary follows the determination of the political power, which has charge of its foreign relations, and is, therefore, presumed to best understand what is fit and proper for the interest and honor of the country.” The prisoner might be a proper subject for extradition, Nelson concluded, but that was a determination that should be made by the executive branch prior to the involvement of the judiciary.

Nelson’s requirement of a prior executive mandate for extradition proceedings became the law of the Second Circuit but was overturned shortly after he retired in 1872. U.S. District Judge Samuel Blatchford (later a U.S. circuit judge and a justice of the Supreme Court) ruled while sitting on the circuit court (In re Thomas (1874)) that no executive mandate was required. Blatchford based his decision on the fact that Congress had issued no such requirement and that judges in other circuits had not followed Nelson’s opinion. The Supreme Court cited Blatchford’s opinion as “the sounder view” in Grin v. Shine (1902).