The United States brought a case against Jacob and Isaac Leflfer for the illegal sale of liquor to Native Americans. The defendants argued that they had not violated any laws because the federal government did not have authority over Indian lands, which was where the transaction took place. The Supreme Court ruled in favor of the United States, stating that Congress has exclusive power over Indian affairs and can regulate trade with them even if it takes place on their own land. This decision established an important precedent regarding tribal sovereignty and set limits on how much control tribes could exercise within their own territories. It also affirmed Congress’s right to pass legislation regulating commerce between Indians and non-Indians without having to consult state governments or other entities first.

In the case of United States v. Jacob and Isaac Leffler, the Supreme Court was asked to decide whether a contract between two parties could be enforced by one party against another despite an intervening act of Congress that made such contracts illegal. The majority opinion held that since Congress had declared such contracts void, they could not be enforced in court. However, Justice McLean dissented from this decision on the grounds that it would lead to injustice for those who entered into these agreements before Congress acted. He argued that if a contract is valid when it is formed and all conditions are met at its formation then it should remain valid even after subsequent legislation has been passed making them illegal; otherwise people will suffer losses due to no fault of their own simply because laws have changed over time. In conclusion, Justice McLean believed that while new laws may make certain types of contracts unenforceable going forward, existing ones should still stand as long as they were legally formed under prior law at the time they were created.