Usually, comparisons between Donald Trump’s America and Nazi Germany come from cranks and internet trolls. But a new essay in the New York Review of Books pointing out “troubling similarities” between the 1930s and today is different: It’s written by Christopher Browning, one of America’s most eminent and well-respected historians of the Holocaust. In it, he warns that democracy here is under serious threat, in the way that German democracy was prior to Hitler’s rise — and really could topple altogether.

Browning, a professor emeritus at the University of North Carolina, specializes in the origins and operation of Nazi genocide. His 1992 book Ordinary Men, a close examination of how an otherwise unremarkable German police battalion evolved into an instrument of mass slaughter, is widely seen as one of the defining works on how typical Germans became complicit in Nazi atrocities.

So when Browning makes comparisons between the rise of Hitler and our current historical period, this isn’t some keyboard warrior spouting off. It is one of the most knowledgeable people on Nazism alive using his expertise to sound the alarm as to what he sees as an existential threat to American democracy.

Browning’s essay covers many topics, ranging from Trump’s “America First” foreign policy — a phrase most closely associated with a group of prewar American Nazi sympathizers — to the role of Fox News as a kind of privatized state propaganda office. But the most interesting part of his argument is the comparison between Senate Majority Leader Mitch McConnell and Paul von Hindenburg, the German leader who ultimately handed power over to Hitler. Here’s how Browning summarizes the history:

Paul von Hindenburg, elected president of Germany in 1925, was endowed by the Weimar Constitution with various emergency powers to defend German democracy should it be in dire peril. Instead of defending it, Hindenburg became its gravedigger, using these powers first to destroy democratic norms and then to ally with the Nazis to replace parliamentary government with authoritarian rule. Hindenburg began using his emergency powers in 1930, appointing a sequence of chancellors who ruled by decree rather than through parliamentary majorities, which had become increasingly impossible to obtain as a result of the Great Depression and the hyperpolarization of German politics. Because an ever-shrinking base of support for traditional conservatism made it impossible to carry out their authoritarian revision of the constitution, Hindenburg and the old right ultimately made their deal with Hitler and installed him as chancellor. Thinking that they could ultimately control Hitler while enjoying the benefits of his popular support, the conservatives were initially gratified by the fulfillment of their agenda: intensified rearmament, the outlawing of the Communist Party, the suspension first of freedom of speech, the press, and assembly and then of parliamentary government itself, a purge of the civil service, and the abolition of independent labor unions. Needless to say, the Nazis then proceeded far beyond the goals they shared with their conservative allies, who were powerless to hinder them in any significant way.

McConnell, in Browning’s eyes, is doing something similar — taking whatever actions he can to attain power, including breaking the system for judicial nominations (cough cough, Merrick Garland) and empowering a dangerous demagogue under the delusion that he can be fully controlled:

If the US has someone whom historians will look back on as the gravedigger of American democracy, it is Mitch McConnell. He stoked the hyperpolarization of American politics to make the Obama presidency as dysfunctional and paralyzed as he possibly could. As with parliamentary gridlock in Weimar, congressional gridlock in the US has diminished respect for democratic norms, allowing McConnell to trample them even more. Nowhere is this vicious circle clearer than in the obliteration of traditional precedents concerning judicial appointments. Systematic obstruction of nominations in Obama’s first term provoked Democrats to scrap the filibuster for all but Supreme Court nominations. Then McConnell’s unprecedented blocking of the Merrick Garland nomination required him in turn to scrap the filibuster for Supreme Court nominations in order to complete the “steal” of Antonin Scalia’s seat and confirm Neil Gorsuch. The extreme politicization of the judicial nomination process is once again on display in the current Kavanaugh hearings. ... Whatever secret reservations McConnell and other traditional Republican leaders have about Trump’s character, governing style, and possible criminality, they openly rejoice in the payoff they have received from their alliance with him and his base: huge tax cuts for the wealthy, financial and environmental deregulation, the nominations of two conservative Supreme Court justices (so far) and a host of other conservative judicial appointments, and a significant reduction in government-sponsored health care (though not yet the total abolition of Obamacare they hope for). Like Hitler’s conservative allies, McConnell and the Republicans have prided themselves on the early returns on their investment in Trump.

This is the key point that people often miss when talking about Hitler’s rise. The breakdown of German democracy started well before Hitler: Hyperpolarization led Hindenburg to strip away constraints on executive power as well as conclude that his left-wing opponents were a greater threat than fascism. The result, then, was a degradation of the everyday practice of democracy, to the point where the system was vulnerable to a Hitler-style figure.

Now, as Browning points out, “Trump is not Hitler and Trumpism is not Nazism.” The biggest and most important difference is that Hitler was an open and ideological opponent of the idea of democracy, whereas neither Trump nor the GOP wants to abolish elections.

What Browning worries about, instead, is a slow and quiet breakdown of American democracy — something more much like what you see in modern failed democracies like Turkey. Browning worries that Republicans have grown comfortable enough manipulating the rules of the democratic game to their advantage, with things like voter ID laws and gerrymandering, that they might go even further even after Trump is gone:

No matter how and when the Trump presidency ends, the specter of illiberalism will continue to haunt American politics. A highly politicized judiciary will remain, in which close Supreme Court decisions will be viewed by many as of dubious legitimacy, and future judicial appointments will be fiercely contested. The racial division, cultural conflict, and political polarization Trump has encouraged and intensified will be difficult to heal. Gerrymandering, voter suppression, and uncontrolled campaign spending will continue to result in elections skewed in an unrepresentative and undemocratic direction. Growing income disparity will be extremely difficult to halt, much less reverse.

I’ve observed this kind of modern authoritarianism firsthand in Hungary. In my dispatch after visiting there, I warned of the same thing as Browning does here: The threat to the United States isn’t so much Trump alone as it is the breakdown in the practice of American democracy, and the Republican Party’s commitment to extreme tactics in pursuit of its policy goals in particular.

We are living through a period of serious threat to American democracy. And Browning’s essay, a serious piece by a serious scholar, shows that it’s not at all alarmist to say so.