A long, long time ago – five decades to be exact – America was roiled by wrenching generational showdowns, massive street protests, and a blazing array of social justice movements. Now, half a century later, similar events and dynamics dominate the public conversation. So, perhaps, it’s poetic that precisely five decades have elapsed since a song that captured all that cultural turmoil, American Pie, became a smash hit. “It’s a song that spoke to its time,” said Spencer Proffer, who has produced a comprehensive new documentary about the song, titled The Day the Music Died. “But it’s just as applicable...