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In September, a New York Times review of a new biography of Adolf Hitler was shared so widely that the 1,000-page book shot up Amazon’s bestseller list. But many people weren’t sharing the article because of what they’d learned about Hitler. The chatter was about the man never mentioned, lurking just between the lines.

The Times book critic, Michiko Kakutani, listed several factors that had helped Hitler rise from a ridiculed rabble-rouser to a nightmarish dictator. She noted that the German leader was an eccentric but compelling speaker who whipped up massive crowds at theatrical rallies, that he was endlessly untruthful and compounded his lies via the latest technologies, that he was an egomaniac who trumpeted slogans about how he alone could make Germany great again and restore law and order, that he exploited economic troubles and popular frustration with political gridlock, that he viewed the world in Darwinian terms and had a thoroughly dark vision of the state of his country, that his opponents and reluctant allies repeatedly downplayed the danger of his demagoguery.

Kakutani described the biography—written by the German historian and journalist Volker Ullrich and focused on Hitler’s life through 1939—as a “parable.” The parable’s lesson, readers quickly concluded, was of the untold hazards of electing Donald Trump president of the United States. It wasn’t the first time during the presidential election that people had compared Trump to Hitler, and it wouldn’t be the last. But Kakutani’s apparent warning, in letting history speak for itself and leaving the rest unsaid, was the most bone-chilling.

History, however, is best read within the lines, not between them. Ullrich’s biography has hundreds of pages of lines, and many of those lines don’t bring Trump to mind. Imagine if, for example, Kakutani had also highlighted Hitler’s military service in a world war, his limited romantic involvement with women, his participation in a violent coup and resulting imprisonment in the 1920s, or the virulently anti-Semitic views he expressed before coming to power in Germany. Readers might not have grasped the implicit message of Kakutani’s article (assuming Kakutani intended her review as an allusion to Trump, which she has neither confirmed nor denied). The signal would have been scrambled.

Ullrich, for his part, had to read Kakutani’s review twice before concluding that it “was intended to do something more than just praise my book.” He doesn’t agree with the subtext that many people spotted.

“I don’t think it’s appropriate to compare Donald Trump with Hitler,” Ullrich told me by email through his translator, Jefferson Chase. “In my opinion, it significantly trivializes Hitler. And as a rule Hitler comparisons are not about fairness. It doesn’t matter whether they’re historically valid or not. They have a political purpose. Hitler is considered the embodiment of evil, so when someone is compared to him, it’s the same thing as rendering a devastating judgment about that person.”

Yet several modern-day political figures have been so judged. Trump’s rival in the U.S. presidential race, Hillary Clinton, once likened Russian President Vladimir Putin’s aggressive tactics to Hitler’s. More recently, Philippine President Rodrigo Duterte responded to claims that he was acting like Hitler in waging a bloody war against drugs by … reinforcing the comparison. Hitler murdered millions of Jews, Duterte noted. “Now, there are 3 million drug addicts [in the Philippines]. I’d be happy to slaughter them.”

In fact, we’re living through a period that is ripe for Hitler comparisons. According to the political scientists Ronald Inglehart and Pippa Norris, “populist authoritarian leaders”—defined as nativist, nationalist, anti-establishment politicians who emphasize the “personal power exerted by strong and charismatic leadership which is thought to reflect the will of the people”—are gaining popularity in democracies around the world. Inglehart and Norris explain the trend as a backlash against transformative social and cultural changes. Other scholars cite factors such as dissatisfaction with dysfunctional politics, economic inequality worsened by globalization and financial crises, and concerns about perceived increases in immigration, crime, and terrorism.

The political scientists Barbara Geddes, Joseph Wright, and Erica Frantz, meanwhile, have found that “personalist dictatorships”—where one person has control over policy, personnel, and security—have grown more numerous since the end of the Cold War. Along with governments dominated by one political party, they are currently the most common form of autocratic regime.

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Personalism has always been part of politics. But the politics of personalism is now ascendant. How, in this age of fear, fragmentation, and rising strongmen, should we apply the lessons of past demagogues and dictators to the present day? And what are the limits of that applied history? As the BBC’s Mark Mardell wrote on Friday, “Is it helpful or pointless that [Hitler’s] memory is used to inform opinions about the rise of the hard right, the growth of Russian nationalism, Dutch politician Geert Wilders and the success of Donald Trump?”

I asked Ullrich for guidance. “What the past offers is an arena of possibilities,” he responded.

“The history of Hitler seems to me to be interesting insofar as his rise illustrates the social conditions and mental preconditions necessary for a charismatic leader of his ilk to have mass success and come to power,” Ullrich told me. “Hitler exploited the profound crisis of the late [interwar German government known as the] Weimar Republic. He knew better than anyone else at the time how to stylize himself into a kind of messiah and to use his audience’s hopes for salvation. You could say that social crisis was his vital elixir. The same is true, mutatis mutandis, for today’s right-wing politicians. They too are products of crisis that they know how to exploit.”

Ullrich’s book attempts to illuminate Hitler as a “human being.” But as cautionary tale rather than the subject of biography, Ullrich seemed to be suggesting, Hitler the man matters less than the context in which he emerged. (That’s not to say today’s crises are on par with those of Hitler’s time, which included the Great Depression and the aftermath of World War I.)

“When he was beginning to rise, Hitler profited from the fact that his opponents were always underestimating him,” Ullrich continued. “That applies to the international level as well. The indecisive and accommodating stance of the Western powers in the 1930s encouraged his aggression. You need to counter politicians like him more quickly and much more forcefully than people back then did with Hitler.”

The challenge is telling the “politicians like him” from the politicians unlike him. Isn’t it difficult, I asked, to be wary of comparing modern-day politicians to historical figures like Hitler while also seeking to stamp out Hitlerian impulses before they spread?

“I don’t see any contradiction,” Ullrich told me. “The word ‘compare’ can mean both ‘equate’ and ‘measure something [against] something else.’ When contemporary politicians are compared with Hitler, what’s meant is always [an] equation intended to generate scandal and stigmatize the person concerned. This political reflex is mostly of little help where the political vigilance you talk about is concerned. And that’s why, aside from their entertaining aspects, I don’t have much regard for such comparisons. But if we speak of comparison in terms of measuring the present day against the historical experience of Hitler, then I think comparisons could help keep us vigilant and make us conscious of the constant threats to freedom and democracy.”

“If the case of Hitler teaches us anything,” he added, “it’s how swiftly democracy can be dismantled, when political institutions fail and civil society is too weak to compensate. The results can be catastrophic.”

Adolf Hitler addresses the German people by radio after being appointed chancellor in 1933. “Hitler’s path to power was anything but inevitable,” Volker Ullrich writes in his biography. As late as 1933, “it would have been eminently possible to prevent his nomination as Reich chancellor.” (Wikimedia)

I mentioned what the historian Timothy Snyder had once told my colleague Edward Delman after publishing a study of the Holocaust. Snyder had noted that Hitler and Ion Antonescu in Romania were both ruthless, anti-Semitic, authoritarian leaders, but that Hitler was operating at a wholly different level than Antonescu in seeking to transform the planet by eliminating the Jews and returning the world to racial struggle. “Looking at [Hitler and Antonescu] in 1938,” Snyder had said, “it may have been difficult to tell the difference,” but “with the distance of history, we can say there was a difference.”

In the present day, is it really possible to precisely sort the Hitlers from the Antonescus, and the Antonescus from less dangerous bigots and authoritarians?

“Hitler possessed a completely different caliber of destructive and criminal energy [than] Antonescu,” Ullrich said. “As early as 1938, it was clear to attentive observers that Hitler wanted to go to war and that his fanatic anti-Semitism put Jews in terrible danger.”

Still, Ullrich allowed that the present day can be blinding: “It is true, however, that this did not apply to the majority of people back then. For them, Hitler’s criminal intentions were only revealed ex post facto. In general, it’s a problem that people don’t have enough imagination to envision what sort of dangers a given politician might present. And only time tells whose estimations were correct. Unfortunately, I can’t offer you a Hitler Identi-Kit.”

What Ullrich did offer was a maxim: Hitler may have been a bully, but “not every bully is a new Hitler. Knowing about the past doesn’t mean you get around carefully scrutinizing the present-day challenges.”

Ullrich appeared to be advocating something similar to what Harvard’s Graham Allison has referred to as the “May Method,” after the late historian Ernest May: Rigorously investigating every historical analogy by listing, in roughly equal proportion, the similarities and differences between the historical analog and the contemporary case (May would ask his students to do this in two columns on a piece of paper).

Consider Ullrich’s view of the Trump-Hitler comparison. “There are certainly several character traits shared by Trump and Hitler,” Ullrich told me. “They include egotism, the tendency to confuse truth and falsehood, resentment of established elites, and their mutual talk of restoring the greatness of their respective countries. By the way, Hitler was also a multi-millionaire who successfully avoided paying taxes.”

Among the numerous differences, however, “Hitler was not only more intelligent. He had a lot more political tricks than Trump. Depending on the situation and social context, he knew how to don various masks and play various roles. He was not just an effective mass speaker, but also a very talented actor. That allowed him to win over various segments of society—not just the insecure middle classes, but parts of the working classes, wealthy bourgeois, and the aristocracy as well.”

Hitler comparisons, according to Ullrich, “don’t always help us better understand contemporary threats. They can do the exact opposite as well.”

The historian Thomas Weber, for instance, has argued that comparing the world’s new strongmen to Hitler creates a “smokescreen,” obscuring more instructive historical analogies. He believes liberal democracies and the world order they collectively built after World War II—free trade, international organizations, international law, etc.—are currently in crisis. And he likens this crisis of liberalism to the crisis that followed the crash of the Vienna stock exchange in 1873, which helped create the conditions in which Hitler, Benito Mussolini, Vladimir Lenin, and Joseph Stalin gradually emerged. “[T]he fact that we do not have to fear the emergence of a new Auschwitz or Hitler-style world war should be no cause for complacency” about reforming liberalism, Weber writes.

Ultimately, Hitler was “a millennial criminal,” Ullrich said. “His name stands for the greatest break with civilization in human history. Without him—here I agree with [the historian] Saul Friedlander—the Holocaust, the single greatest crime against humanity, would have been inconceivable. And without him the German military campaign against the Soviet Union would not have become an unprecedented racist war of annihilation. It’s scarcely conceivable that something similar could recur. But that doesn’t rule out serious crimes against humanity in the future. Some have already occurred [since] 1945.”

Neither Rodrigo Duterte nor Vladimir Putin nor Donald Trump is Hitler. They are, respectively, Rodrigo Duterte, Vladimir Putin, and Donald Trump. History demands that they be taken seriously on their own merits and measured against the past’s spectrum of possibilities. Among those possibilities are many examples of the damage strongmen can do to democracy.