“ In time he became prominent as a Democratic politician, and from 1845 to 1851 was a member of the National House of Representatives. Although elected as a Democrat, he opposed the extension nf slavery into the territory that it was expected the United States would acquire from Mexico, and in 1846 he moved his famous amendment, known as the Wilmot Proviso (q.v.) . In 1848 he supported Van Buren for the Presidency instead of the regular Democratic candidate, and afterwards became a Republican. ”