Question: Robert Nelson Cornelius Nix Sr., was an American politician who served in the United States House of Representatives from 1958 until 1979, he was the first African American to represent Pennsylvania in the House of Representatives, the first African Americans to serve in the United States Congress were Republicans, elected during which time period?
Sentence (from "African Americans in the United States Congress"): By the presidential election of 1876, only three state legislatures were not controlled by white Democrats.
Relevant evidence: No