After following his father into the local politics of his home county, Clements agreed to chair the gubernatorial campaign of Thomas Rhea in 1935. Already committed to Rhea, he turned down an offer from Happy Chandler to chair his campaign, beginning the rift between the two men. Clements went on to the Kentucky Senate in 1941. In 1944, he was selected as Democratic floor leader of the senate and successfully campaigned for a larger budget than that proposed by Republican governor Simeon Willis. His stand against Willis made him popular in the Democratic Party, and he went on to serve two terms in the U.S. House of Representatives from 1944 to 1948.