In United States vs. Jackalow, the Supreme Court ruled that a defendant could not be convicted of an offense if it was committed in a state where it was legal at the time. The case involved John Jackalow, who had been charged with selling liquor to Native Americans on Indian reservations in Minnesota and Wisconsin without obtaining permission from local authorities as required by federal law. However, when he committed this act both states allowed such sales without requiring any license or permit from local authorities. Therefore, the court held that since his actions were lawful under state law at the time they occurred he could not be found guilty of violating federal laws prohibiting such activity on Indian reservations. This ruling established important precedent for future cases involving conflicts between state and federal laws regarding criminal offenses.

In United States vs. Jackalow, the Supreme Court was asked to decide whether a federal court had jurisdiction over an alleged violation of a treaty between the United States and Creek Nation. The majority opinion held that it did not have such jurisdiction because treaties are considered "the supreme law of the land" under Article VI of the Constitution, but this does not give federal courts exclusive authority to enforce them. Justice Field dissented from this opinion, arguing that Congress has given federal courts exclusive power to hear cases involving violations of treaties with Native American tribes and that there is no reason why they should be treated differently than any other contract or agreement between two parties. He further argued that if Congress intended for state courts to have concurrent jurisdiction in these matters then it would have explicitly stated so in its legislation granting authority to federal courts on Indian affairs.