"Waving the bloody shirt" was the phrase once used to describe the standard demagogic tactic of the late 19th century, when memories of the Civil War were still vivid and loyalists of both parties could be moved to "vote as they shot." As the years passed and the memories faded, the shirt got gorier, the waving more frantic.

In 1896 the Democrats chose William Jennings Bryan as their leader, a man who was born in 1860 and had thus missed the Civil War, but who seemed to threaten the consensus politics of the time. In response,...