This August will mark Leonard Bernstein’s 100th birthday. The centenary celebrations started last August and are worldwide. The Bernstein estate counts more than 2,000 events on six continents. And there is plenty to celebrate. But if Bernstein remains a figure of limitless fascination, it is also because his story is archetypal. He embodied a tangled nexus of American challenges, aspirations, and contradictions. And if he in some ways unraveled, so did the America he once courted and extolled.