He remained active in Republican politics and worked to liberalize and broaden the face of the party in Dade County and throughout the state. In 1962 he managed the congressional campaign of Republican newcomer Robert A. Peterson against Claude Pepper. Peterson lost, but Cain established himself as a viable political force in Florida. He considered running for the U.S. Senate in 1964 and again in 1968, but his moderate positions on social issues were in variance with the state party. He chaired the Florida Citizens for Johnson-Humphrey, the Democratic Party ticket, in 1964, but supported Nelson Rockefeller and then Richard Nixon in 1968 based on his opposition to the Vietnam War. In 1972, he supported his old opponent, Henry Jackson, for the Democratic presidential nomination and campaigned with him in Florida.