In 1903, Johnson succeeded in taking control of the state Democratic Party, an effort which Clarke supported. At the party's convention that August, Clarke was nominated as the Democratic candidate for the United States Senate. Though an accomplished orator, Clarke's work as a railroad attorney, his opposition to Bryan's presidential candidacy seven years before, and his own personal limitations all contributed to his failure to upset his Republican rival, Mark Hanna, who won the balloting in the Ohio General Assembly by 115 votes to 25 for Clarke.