By conventional understanding, a collaborator is one who assists an enemy, helping groups to which he does not belong threaten groups to which he does belong. But this definition, it seems to me, is too restrictive. It presumes that a group is a discrete whole, that once in it, we can’t get out of it or have competing affiliations. Collaborators, however, cannot be so neatly bound. Some do not entirely belong to the group they betray; others, like the French fascists of Vichy, have a deep affinity for the enemy they aid. Informers are perhaps the most common kind of collaborator, but they are notorious chameleons, making it virtually impossible to pin down their affiliations at all.

Knud Wollenberger, an East German dissident who secretly kept the Stasi apprised of his wife’s subversive activities, claims that his collaboration was entirely consistent with his membership in the couple’s oppositional circle. One way to challenge the government, he explains, was “through open dissidence, and the other way [was] through government channels. I was on the inside and the outside at the same time.” Harvey Matusow joined the American Communist Party in 1947, began informing on it in 1950, recanted his testimony in 1954, and then lied about all three phases of his career in his memoir False Witness, published in 1955. So promiscuous were Matusow’s politics, it is impossible to know what he had been false to, except the truth. The title of another FBI informant’s memoir—I Led Three Lives (as Communist, informer, and “citizen”)—was more apt, suggesting the multiple identities the collaborator regularly assumes.

I don’t wish to carry this notion of multiple affiliations too far. Wollenberger could very well be rationalizing a past of which he is ashamed, and Matusow may simply be the hollow man many at the time suspected him to be. Whether we belong to one group or another in some existential sense, in the course of our lives we do incur moral obligations to our comrades and friends, whom we betray when we aid our opponents.

But to avoid the question of identity that restrictive definitions of collaboration entail, I will use the definition contained in the word’s Latin root collaborare: “to work together.” By collaborator, I simply mean those men and women who work with elites and who occupy the lower tiers of power and make political fear a genuinely civic enterprise. Collaborators may be low- or mid-level perpetrators; suppliers, like the warehouse in Jedwabne, Poland, which provided the kerosene local residents used in 1941 to burn a barn containing 1,500 Jews, or Ford and General Motors, which funded a Brazilian security outfit that interrogated and tortured leftists; attendants (cooks, secretaries, and other supporting staff); or spies and informers. Though all are not equally compromised by their deeds, each is guilty of complicity.

The collaborator is an elusive figure. With the exception of The Persian Letters and Eichmann in Jerusalem, he seldom makes an appearance in the literature of political fear. One of the reasons for his absence, I suspect, is that he confounds our simple categories of elite and victim. Like the elite, the collaborator takes initiative and receives benefits from his collaboration. Like the victim, he may be threatened with punishment or retribution if he does not cooperate.

Many collaborators, in fact, are drawn directly from the ranks of the victims. Perhaps then we can distinguish between collaborators of aspiration, inspired by a desire for gain, and collaborators of aversion, inspired by a fear of loss. The first are akin to elites, the second to victims. But even that distinction is too neat. Elites also fear loss, and victims hope for gain, and as the economist’s notion of opportunity costs attests, the hope of gain often informs the fear of loss.

Collaborators serve two functions. First, they perform tasks that elites themselves cannot or will not perform. These tasks may be considered beneath the dignity of the elite: cooking, cleaning, or other forms of work. They may require local knowledge—as in the case of informers, who provide information elites cannot access on their own—or specialized skills. We often think of torturers, for example, as thugs from the dregs of society. But torture is a weapon of knowledge, designed to extract information from the victim, often without leaving a physical trace. The torturer must know the body, how far he can go without killing the victim. Who better to assist or direct the torturer than a doctor? Thus, 70 percent of Uruguayan political prisoners under that country’s military regime claim that a doctor sat in on their torture sessions.

Second, collaborators extend the reach of elites into corners of society that elites lack the manpower to patrol. These collaborators are usually figures of influence within communities targeted by elites. Their status may come from the elite, who elevate them because they are willing to enforce the elite’s directives. More often, their authority is indigenous. Figures of trust among the victims, they can be relied upon to persuade the victims not to resist, to compound the fear of disobedience the victims already feel. During its war against leftist guerillas in the late ’70s and early ’80s, the Salvadoran army worked closely with such indigenous leaders. In 1982, a battalion officer informed Marcos Díaz, owner of the general store in the hamlet of El Mozote, with friends in the military, that the army was planning a major offensive in the region. To ensure their safety, the officer explained, the townspeople should remain in the village. Though many in El Mozote thought such advice unsound, Díaz was the local potentate who knew the army’s ways. His voice held sway, the villagers did as they were told, and three days later, some eight hundred of them were dead.

Because their functions are so various, collaborators come in all shapes and sizes. Some travel in or near the orbit of elite power; others are drawn from the lower orders and geographic peripheries. One common, though unappreciated, influence upon their actions is their ambition. While some collaborators hope to stave off threats to their communities and others are true believers, many are careerists, who see in collaboration a path of personal advance. In Brazil, for example, torture was a stepping stone, turning one man into the ambassador to Paraguay and another into a general, while doctors advising the torturers in Uruguay could draw salaries four times as high as those of doctors who did not.

Whether the payment is status, power, or money, collaboration promises to elevate men and women, if only slightly, above the fray. Nazi Germany’s Reserve Police Battalion 101, for example, was a unit of five hundred “ordinary men,” drawn from the lower middle and working classes of Hamburg, who joined the battalion because it got them out of military service on the front. All told, they were responsible for executing 38,000 Polish Jews and deporting some 45,000 others to Treblinka. Why did they do it? Not because of any fear of punishment. No one in the 101 faced penalties—certainly not death—for not carrying out their mission. The unit’s commander even informed his men that they could opt out of the killing, which 10 to 15 of them did.

Why did the remaining 490 or so stay? According to Christopher Browning, there were different reasons, including anti-Semitism and peer pressure, but a critical one was their desire for advance. Of those who refused to kill Jews, in fact, the most forthright emphasized their lack of career ambitions. One explained that “it was not particularly important to me to be promoted or otherwise to advance.… The company chiefs … on the other hand were young men and career policemen who wanted to become something.” Another said, “Because I was not a career policeman and also did not want to become one … it was of no consequence that my police career would not prosper.”

Though ambitious collaborators like to believe that they are adepts of realpolitik, walking the hard path of power because it is the wisest course to take, their realism is freighted with ideology. Careerism has its own moralism, serving as an anesthetic against competing moral claims. Particularly in the United States, where ambition is a civic duty and worldly success a prerequisite of citizenship, enlightened anglers of their own interest can easily be convinced that they are doing not only the smart thing, but also the right thing. They happily admit to their careerism because they presume an audience of shared moral sympathy.

How else can we understand this comment of director Elia Kazan in response to a colleague’s request that he justify his decision to name names? “All right, I earned over $400,000 last year from theater. But Skouras [the head of Twentieth-Century Fox] says I’ll never make another movie. You’ve spent your money, haven’t you? It’s easy for you. But I’ve got a stake.”

This is the fourth in a series of five posts this week on fear in the age of Trump, drawn from Fear: The History of a Political Idea.