Klan leaders used that stunning success to insinuate the Invisible Empire into public life. On the local level, Klansmen turned themselves into moral watchdogs: beating drunken husbands, whipping wayward wives, chasing down bootleggers and purifying public schools, mostly by demanding that Catholic teachers be fired. In Indiana, Oregon, Colorado, Texas and Arkansas they built political machines strong enough to put their hand-picked candidates into governors’ offices. Indiana’s K.K.K. took control of the State Legislature, too, while Texas sent a Klansman to the United States Senate. There was even talk in the highest circles of trying to elect a Kluxer president.

Then everything came apart. The immediate cause was a sex scandal that swept through the Klan in the early months of 1925. But the K.K.K. was already collapsing, Pegram says, its rank and file pulling away from its leaders’ oversize ambitions. Drawing on a range of local studies, he argues that most Klansmen didn’t want anything more than a bit of fraternal intolerance — the chance to bond with their Protestant brethren, wear flashy outfits and complain about the country’s going to hell — just as Simmons had thought. They had no interest in whipping anyone; that was the work of the Klan’s bully boys, the militant minority who in another setting would have been wearing brown shirts. Many klaverns ignored their leaders’ political directives. Others splintered into rival factions. And almost everywhere, knights complained that the central office was more interested in making money than in saving America.

Pegram is at his best exploring the problems that bedeviled the Klan. He’s not a supple writer. But he’s got an eye for the telling detail: the organizer who mistakenly wandered into a meeting of the Knights of Columbus and came away convinced that Catholics weren’t the threat the K.K.K. claimed them to be; the Ohio klavern that bombed its own headquarters so it would appear to be under assault; the Texas Klansman who left a grim meeting in 1925 so disgusted with the order’s incompetence he put his robes down by the side of the road and set them on fire. He wasn’t alone. In the late 1920s Klan membership tumbled, klaverns closed and the Invisible Empire settled into the dustbin of history, Pegram says, while the pluralism it had railed against marched inexorably onward.

That’s not the way Kelly J. Baker sees it. In form, her book, “Gospel According to the Klan,” is far narrower than Pegram’s, in execution much weaker. A religious studies professor at the University of Tennessee, Baker concentrates not on the Klan’s institutional dynamics but on its embrace of militant Protestantism, which she argues shaped Klansmen’s understanding of their world and the threats it faced. That’s hardly a revelation; this was an organization that spent a lot of time setting crosses on fire, after all. But Baker works it as hard as she can. While Pegram builds his book up from the experiences of ordinary Klansmen, she builds out from the Klan’s official declarations of religious devotion drawn from K.K.K. newspapers and magazines. In large part, “Gospel According to the Klan” is an exegesis of these less-than-sacred texts, a painstaking analysis of the banal. The results are less than spectacular. Having walked us through a series of Kluxer tributes to their mothers, for instance, Baker tells us that “the Klan’s vision of motherhood revolved around the female figure, who sustained the order and fostered her children regardless of her own interests.”

At the end of the book, though, Baker steps back from her texts. Suddenly her analysis becomes more pointed. Yes, the Klan had a very short life. But it has to be understood, she contends, as of a piece with other moments of fevered religious nationalism, from the anti-Catholic riots of the antebellum era to modern anti-­Islam bigots. Indeed, earlier this year, Herman Cain declared that he wouldn’t be comfortable with a Muslim in his cabinet. It’s tempting to see those moments as Pegram does the Klan: desperate, even pitiful attempts to stop the inevitable broadening of American society. But Baker seems closer to the mark when she says that there’s a dark strain of bigotry and exclusion running through the national experience. Sometimes it seems to weaken. And sometimes it spreads, as anyone who reads today’s papers knows, fed by our fears and our hatreds.