The United States v. M'Dowel was a Supreme Court case that addressed the issue of whether or not an individual could be tried for treason in two different states. The defendant, M'Dowel, had been accused of treason against the United States by both Virginia and Pennsylvania. He argued that he should only have to face one trial as it would violate his constitutional rights if he were tried twice for the same crime. The Supreme Court ultimately ruled in favor of M'Dowel and held that double jeopardy applied even when multiple states were involved; thus, individuals cannot be charged with the same offense more than once regardless of which state is prosecuting them. This decision established important precedent regarding double jeopardy protections under federal law and has since been cited numerous times throughout legal history as a key example of how these protections apply across state lines.

In United States v. M'Dowel, the Supreme Court was asked to decide whether a federal court had jurisdiction over an offense committed on board of a vessel in navigable waters within the limits of a state. The majority opinion held that Congress did not have authority to punish such offenses and thus the federal court lacked jurisdiction. Justice Samuel Chase dissented from this decision, arguing that Congress has power under Article I Section 8 Clause 10 of the Constitution to make all laws necessary and proper for carrying into execution its powers vested by law in any department or officer thereof. He argued that since it is part of Congress's duty to provide for punishing crimes against public justice, they should be able to do so even if those crimes are committed on board vessels in navigable waters within states’ boundaries. Thus he concluded that there was no reason why Congress could not exercise their power over these types of offenses as well as others and therefore the federal court had jurisdiction over them too.