From patriotic poetry to equestrian monuments, most of the instruments that once elevated war and national tragedy into the realm of collective experience have lost their power to stir us. There is no contemporary counterpart to the Civil War’s “Battle Hymn of the Republic” or Norman Rockwell’s mass-produced prints of the “Four Freedoms” from World War II. A song like “Over There,” to which America marched briskly in 1917, is as remote to contemporary sensibilities as the Bayeux Tapestry. The only artistic medium that now seems capable of informing the national mind about the shape and meaning of events is...