Imagine a political movement created in a moment of terrible anxiety, its origins shrouded in a peculiar combination of manipulation and grass-roots mobilization, its ranks dominated by Christian conservatives and self-proclaimed patriots, its agenda driven by its members’ fervent embrace of nationalism, nativism and moral regeneration, with more than a whiff of racism wafting through it.

No, not that movement. The one from the 1920s, with the sheets and the flaming crosses and the ludicrous name meant to evoke a heroic past. The Invisible Empire of the Knights of the Ku Klux Klan, they called it. And for a few years it burned across the nation, a fearsome thing to ­behold.