McKinley v. Wheeler was a Supreme Court case that was decided in 1891. The case involved a dispute between two parties over a contract for the sale of a steamboat. The plaintiff, McKinley, had contracted with the defendant, Wheeler, to purchase a steamboat for $2,000. After the contract was made, McKinley paid Wheeler $1,000 as a down payment. However, Wheeler refused to deliver the steamboat and McKinley sued for breach of contract. The Supreme Court held that the contract was valid and enforceable. The Court found that the contract was supported by consideration, as McKinley had paid Wheeler $1,000 as a down payment. The Court also found that the contract was not voidable due to any lack of capacity on the part of either party. The Court held that McKinley was entitled to damages for the breach of contract, and ordered Wheeler to pay McKinley the $2,000 that was agreed upon in the contract.

In the case of McKinley v. Wheeler, Justice Harlan delivered a dissenting opinion in which he argued that the majority's decision was inconsistent with previous Supreme Court decisions and undermined Congress' power to protect citizens from discrimination. He noted that while it is true that states have broad powers to regulate their own affairs, they do not have absolute authority over matters involving civil rights or other fundamental interests protected by the Constitution. Furthermore, he argued that if Congress had intended for state law to be controlling in this matter then it would have explicitly stated so when passing legislation on the subject. In conclusion, Justice Harlan asserted that allowing states to override federal laws protecting individuals from discrimination would lead to an unjust result and should therefore be rejected by the court.