The view from the National Hotel dollar bar.

The value of vengeance is the anxiety it creates in those who witness it. The anxiety at any moment can become fear, and then terror.

Consider the case of an acquaintance of mine, a freshly minted American correspondent in Moscow who liked to hang out at the National Hotel dollar bar overlooking the Kremlin. It was called the dollar bar in those Soviet days because it accepted only dollars, or pounds, or francs—not rubles. So the customers were foreigners—mainly businessmen and reporters—and the occasional young woman eager to be invited for a drink.

My friend, who will remain nameless because I’m no longer in touch with him, was experienced enough to recognize an obvious set-up but succumbed nonetheless and invited the lady for a drink, then to his apartment. More than once.

Then late one night there came a knock at his door. Anxiety. The visitor identified himself as a KGB officer and told the reporter that the young lady he’d been sleeping with was the officer’s daughter and that she was pregnant. Fear. There were, however, ways in which the reporter might make himself helpful, the visitor said before leaving.

The reporter, now terrified, fled to the U.S. embassy where he stayed for a couple of weeks, communicating with his employer over the embassy’s secure phone. Eventually embassy staff drove him to the airport and put him on an airplane bound for America.

One of the KGB’s full-time functions was to identify foreigners who had personal needs—for money, sex, flattery—any weakness that could make them vulnerable to blackmail. Once turned they could become spies, purveyors of disinformation, agents of influence inside their country’s government. The Russians called them polezniye duraki—useful fools. In his early KGB days Vladimir Putin, fluent in German, monitored foreigners for that purpose in Leningrad, now St. Petersburg. The KGB’s successor organization under Putin, the FSB, does the same.

What happened to my acquaintance was blackmail, not vengeance. What Donald Trump employs against adversaries is vengeance. He understands exploiting weakness. As David Brooks put it, Trump’s “primary thing is bashing enemies.” Or as Bill Maher told Jim Rutenberg of The Times, Trump “lives for vengeance.”

But just as anxiety, fear, and terror are first cousins, so are blackmail and vengeance. Blackmail is possible because of the fear of vengeance. Both thrive on uncertainty. If Trump shuts down CNN as he did at his Wednesday press conference by refusing to hear a question from Jim Acosta, can’t he shut down other news organizations he doesn’t like and for longer?

My colleagues in Moscow stayed away from the National Hotel dollar bar. Jim Acosta’s colleagues in Washington rallied in support of him. But Moscow and Donald Trump each hold more potential for vengeance and terror than any handful of reporters.