Derek Black didn’t become a white supremacist. He was born one. His father, Don Black, was a former Grand Wizard of the Ku Klux Klan and the creator of Stormfront, one of the most popular white-nationalist Web sites in the United States. Derek’s mother, Chloe, had previously been married to David Duke, America’s leading neo-Nazi and Derek’s godfather. Smart, articulate, and savvy, Derek co-hosted a radio show with his father, addressed conferences, and wrote articles on the Web. From an early age, he knew how to package racism for a crowd that was warm to the message but uncertain about its implications. He didn’t argue for the supremacy of whites. He said that whites were a group, one of many, that had the right, like other groups, to defend its interests and identity. Races weren’t unequal; they were different. White nationalists were the “true multiculturalists.” He had his dad scrub Stormfront clean of Nazi signs and racial epithets. Press too hard, speak too crudely, you’ll lose people. All things in moderation.

A gifted code-switcher, Derek had the ability—strangely not rare among racist demagogues—to understand and relate to people who weren’t like him. That came in handy in 2010, when he enrolled at the liberal New College, in Sarasota, Florida. New College dispensed with grades and large lectures, and it appealed to the homeschooled and bookish Derek, who wanted to pursue a double major in German and medieval history. He kept quiet about his family and his beliefs. He blended in, hanging out with Juan, an immigrant from Peru, and Matthew, an Orthodox Jew from Miami. He even dated a Jewish student named Rose. At the end of his spring semester, the idyll of experiment and anonymity came to an end. A senior who was writing his thesis on right-wing paramilitaries outed Derek on an online campus forum. Derek was condemned by friends, flipped off by strangers, and kicked out of student clubs. Campus activists debated whether he should be expelled, ostracized, or shamed. Rose broke up with him.

Matthew took a different course. He began hosting weekly Shabbat dinners, which Derek, Juan, and other students attended. Matthew’s only rule, which he explained to everyone but Derek, was “Don’t be assholes. We want him to come back.” For months, one of Matthew’s roommates, Allison, steered clear of Derek and the dinners. Then she started talking to Derek, who turned out to be kind, chill, and a good listener. They hung out, a lot. She became some combination of girlfriend, therapist, amanuensis, prosecutor, and priest. She saw that Derek took pride in his intellect, and that he believed in logic and evidence. So she plied him with data about racial discrimination, income disparities, the bias in I.Q. tests, and so on, daring him to follow the facts wherever they led.

It worked. By the time he graduated from New College, Derek no longer believed in white nationalism. As Eli Saslow reports in “Rising Out of Hatred,” his numinous account of Black’s transformation, it wasn’t only Allison’s engagement and Matthew’s dinners that produced the change. The hostility of activists and other students contributed as well. The combination of conversation and callout, friendship and confrontation, inquisition and inclusion—all the contradictory elements of today’s college campuses—pressed Derek to examine and abandon his beliefs. It helped that he was an excellent student, who professors encouraged to pursue an academic career. Was an ideology he was no longer sure of worth the price of social exclusion?

Allison, though, insisted that it wasn’t enough to give up white nationalism. Having contributed so much to its rise, Derek was obligated to push for its fall. After George Zimmerman was acquitted of the murder of Trayvon Martin, in 2013, Derek wrote a goodbye letter to the movement he had grown up in. It was published by the Southern Poverty Law Center, a longtime nemesis of David Duke and Don Black. Don was furious. For days, he bombarded Derek with calls, text messages, and e-mails. Derek, he said, had betrayed him. His actions were “nails to the heart,” leaving wounds so deep that they’d never be healed. In his final hour of need, the neo-Nazi father had become a Jewish mother.

The political convert was the poster child of the Cold War. The leading ideologues of the struggle against Communism weren’t ancient mariners of the right or liberal mandarins of the center. They were fugitives from the left. Max Eastman, Arthur Koestler, Whittaker Chambers, Sidney Hook, James Burnham, and Ignazio Silone—all these individuals, and others, too, had once been members or fellow-travellers of the Communist Party. Eventually, they changed course. More than gifted writers or tools of Western power, they understood what Edmund Burke understood when he launched his struggle against the French Revolution. “To destroy that enemy,” Burke wrote of the Jacobins, “the force opposed to it should be made to bear some analogy and resemblance to the force and spirit which that system exerts.”

The ex-Communists knew the appeal of Communism. Any movement to counter it would have to offer an equivalent fare. Conservatives could provide the guns; liberals and socialists the butter. Only the ex-Communist could supply the spirit. “All you comfortable, insular, Anglo-Saxon anti-Communists,” Koestler said to Richard Crossman, the editor of the influential anthology “The God That Failed,” “resent us as allies—but, when all is said, we ex-Communists are the only people on your side who know what it’s all about.” Under the tutelage of the ex-Communists, anti-Communism achieved a fullness that almost mirrored Marxism itself. It had a sociology of the problem, but instead of classes and capitalism there were intellectuals and the Party; these were the enemies to be fought and overthrown. It had a political theology, but instead of revolution and ideology there were repentance and the end of ideology (or Christianity, in the case of Chambers). It had a program, too: not containment but rollback.

Then something happened. The further the conversion got from the original moment of the Bolshevik Revolution, the staler the story became. Isaac Deutscher, Trotsky’s biographer and a committed anti-Stalinist of the left, was probably the first to notice the diminished quality of later defections. Comparing the testimony of Silone, who helped create Italy’s Communist Party in the aftermath of 1917, to that of Koestler, who joined Germany’s Stalinized Communist Party in the nineteen-thirties, Deutscher observed that Silone had the opportunity to be “a revolutionary before he became, or was expected to become, a puppet.” Koestler, on the other hand, began his “experience on a much lower level.” Silone built a movement; Koestler got an assignment. The “sterility of the party’s first impact” on him and on others who came after him found its way into their anti-Communism.

There’s a similar declension in the odysseys of the six converts profiled by Daniel Oppenheimer in his engaging study “Exit Right: The People Who Left the Left and Reshaped the American Century.” In the stories of Chambers, Burnham, and even Ronald Reagan, who also began his career on the left, the electricity of their right turn is palpable. With the latecomers—Oppenheimer looks at Norman Podhoretz, David Horowitz, and Christopher Hitchens, all of whom joined the left between the nineteen-fifties and sixties—the lights dim. The personal narratives of Chambers, Burnham, and Reagan opened out onto a larger landscape of politics and culture; the narratives of Podhoretz, Horowitz, and Hitchens are small stories of the self. Chambers and Burnham wrote about their ex-Communism, Podhoretz about his ex-friends. (He even called one of his books “Ex-Friends.”) It wasn’t for lack of topic: Podhoretz in his day could be as self-loathing as Chambers. Nor was it for lack of talent: Hitchens was easily the best writer of the bunch. But someone’s “date of joining” the left, as Deutscher drily noted, “is relevant to their further experience.” Musty movements make for airless apostasy. The poster child becomes the problem child.