 Clark, who had promised to serve as mayor for only one term, announced his candidacy for the United States Senate in 1956.After winning the Democratic nomination over the opposition of Philadelphia's party leaders, he faced first-term Republican incumbent James H. Duff, a popular former governor, in the general election.During the campaign, Clark ran on a liberal platform which included support for increasing the minimum wage, expanding Social Security, and repealing the Taft–Hartley Act.