In the United States v. Mosley case of 1914, the Supreme Court ruled in favor of protecting voting rights under federal law. The defendant, William S. Mosley was a Kentucky election official who had denied African American citizens their right to vote in a congressional primary election. He argued that his actions were not subject to federal jurisdiction as they pertained only to state elections and not national ones; thus he could not be prosecuted under Section 19 of the Criminal Code which protects against conspiracy to infringe upon civil rights (including voting). However, the Supreme Court disagreed with this argument stating that all elections where representatives are chosen for Congress fall within its purview regardless if it's a primary or general election - thereby upholding federal protection over individual voting rights even at state level primaries.

In the dissenting opinion for United States v. Mosley, Justice Holmes argued that the majority's interpretation of the Enforcement Act was too broad and overstepped its intended purpose. He contended that while Congress had a right to enforce laws regarding federal elections, it did not have authority over state election processes unless there were clear violations of civil rights or constitutional provisions. According to him, this case involved only an alleged violation of state law - failing to count votes in a primary election - which fell outside federal jurisdiction. Therefore, he believed that no crime under U.S law had been committed by Mosley and his co-defendants when they allegedly failed to count certain ballots during a local Democratic primary in Kentucky because primaries were not covered by existing federal legislation at that time.