Country music has been having an identity crisis since it crawled out of the cradle. Call it diffuse or call it elastic, but it has always run on two tracks: one was rough and one was slick, one rooted in tradition, the other more modern. Think about that serendipitous August in 1927 in Bristol, Tennessee, when, two days apart, both Jimmie Rodgers and the Carter Family auditioned for the Victor Talking Machine Company (which would ultimately become RCA Records). Ralph Peer, the record company’s producer and talent scout, immediately signed both acts. That was a big week for country...