Johnny Cash runs for Governor of Tennessee in 1974, defeating Ray Blanton in the Democratic primary. His term as governor is successful due to bringing economic development to the state as well as raising the profile of Tennessee in general for tourism and other investment. As he is he term-limited, he leaves office in 1982, where he has a brief comeback in his music career before his 1984 Senate run where he defeats Al Gore in the primaries for the Democratic nominee for Senator, and comfortably wins Howard Baker's vacated Senate seat. In the 1992 election, he becomes the Democrat nominee for president and beats George H.W. Bush to become president, likewise winning re-election in 1996. Johnny Cash dies around the same time as IOTL.
Really depends how much the Man in Black wants to work with other Tennessee political figures, but once he's in there he'd likely be able to convincingly attribute a lot to his governorship and Senate terms to attract voters both statewood and in the national primaries. Plus he has that name recognition which is always good. His religious and political beliefs will sync well to appeal to many voters.