The truth is that the greatness of American art during this period lay mostly beyond the traditional media of painting and sculpture, which means this show shines brightest at its edges. Two of its most ravishing moments remind us that the movies are the dominant art form of the 20th century, American or otherwise: Fred Astaire and Ginger Rogers's meltingly beautiful skipping dance to Cole Porter's "Night and Day" in The Gay Divorcee, and Busby Berkeley's ecstatically lunatic choreography in Gold Diggers of 1933, featuring dancing girls who form ornate, pulsating patterns while playing neon violins.
One of the show's greatest missed opportunities shows up in the final galleries, where this ponderous saga peters out in the art of the abstract expressionists, among a handful of small, not always stellar works. There is, for example, no late-1940s black-and-white de Kooning and only one work each by Pollock, Kline, and Still. In the hollowness of these galleries, other possibilities come to mind. The idea that occurred to me was that during the 1940s some of the most creative American outsider artists of the century were working or beginning to work, among them Martin Ramirez, Henry Darger, A.G. Rizzoli, and Bill Traylor, a freed slave. They weren't known at the time, but they deserved to be and now they are. Evidently, that would have been going too far for the Whitney, an institution that seems content with the same old American century.