Elizabeth Kübler-Ross is best known for her five stages of grief on dealing with a fatal illness. The first reaction, the first stage of grief, is denial. You can’t believe this is happening. It is only temporary. It is not as bad as it seems. Then comes anger. It is not going away. It is getting stronger; you are getting weaker. It’s spreading. The next stage is bargaining. There is a way to stop this. It can be controlled. It’s just a matter of finding the right way to interact with it, to limit its ambitions. And then there is despair. It’s not going to work. You’re going to lose, and you’re going to lose everything. Finally, there is acceptance. As long as it’s going to happen, you might as well get behind it, if you can, if it lets you. You know it’s going to feel much better than the alternative, which is trying to struggle against it, and be painfully destroyed. Or admit defeat, and remove yourself, as far away as possible, to a place of safety.

I am talking about, of course, the stages of grief and mourning that accompanied the rise to power of Adolf Hitler. It was eminently preventable. His slow ascendance was telegraphed way in advance. He let people know what he wanted to do, and what his goals were. There was opposition, of course, internal and external, but his opponents were divided, and probably never took the threat with sufficient seriousness. People thought they could control him; people thought that the responsibilities of governing would temper his excesses. People thought that his rhetoric was just that, letting off steam, that he was a loudmouthed and foulmouthed Antisemite, but people would eventually see through him. That he was too incompetent, too inexperienced to govern by himself, that wiser and cooler heads would eventually prevail. Or that if they supported him, he would return the favor. Or perhaps, that his bark was worse than his bite, and that he couldn’t really believe his own rhetoric.

When, if you got your news from the pages of the New York Times, would you first have heard the name Adolf Hitler? It probably would have been on 21 November, 1922, in the earliest article about Hitler in the paper. The article, entitled, “New Popular Idol Rises in Bavaria: Hitler Credited with Extraordinary Powers of Swaying Crowds to His Will,” stated that “Der Hitler has been called the Bavarian Mussolini and his followers the Bavarian fascisti” and that Hitler and his “Hakenkreuzers”—the word Nazi does not appear in the article—“are the popular topic of talk in Munich.” Those reading the article would have no doubt about Hitler’s “reactionary Nationalist anti-Semitic movement,” its physical violence against opponents and rhetorical violence against Jews. The article stated that “he probably does not know what he wants to accomplish,” but added that Jews in Munich were worried about “an anti-Semitic St. Bartholomew’s night,” a reference to the massacre of French Protestants by French Catholics in 1572. That is to say, in the very first article about Hitler in the New York Times, there was a reference to his possible mass-murder of Jews. But the author of the article couldn’t quite believe his own reportage. He added that “several reliable, well-informed sources confirmed the idea that Hitler’s anti-Semitism was not so genuine or violent as it sounded, and that he was merely using anti-Semitic propaganda as bait to catch masses of followers.” He wasn’t alone in thinking this. It was hard to imagine that this comical, strutting buffoon really meant what he said, much less that he would become ruler of Germany, and would actually have the power to try to realize his plans for the Jews.

And so, Hitler went on his way, with the Beer Hall Putsch, writing Mein Kampf, winning election after election, making blood-curdling threats against the Jews. And on 30 January, 1933—the darkest day in German, if not world history—Hitler became chancellor of Germany. And the New York Times still couldn’t quite believe what was happening. With less justification than in 1922, the Times was still writing about Nazism as a phenomena that was less threatening than it really was. The Times’s lead article was headlined, “Hitler Puts Aside Aim to be Dictator.” It opened: “Adolf Hitler’s acceptance of the German Chancellorship in a coalition with conservative and non-partisans marks a radical departure from his former demand that he be made the ‘Mussolini of Germany.’”

But I am not just writing about Adolf Hitler. I am writing about Donald Trump. Yes, the comparison is totally unfair. It ends the conversation. We need to write about the Trump phenomena without hyperbole. And of course, in comparison to Hitler, everyone is an angel, even Josef Stalin—a leading candidate for the title of the second most evil man who ever lived—who, as long as he was fighting Hitler, was angelic. My point is that it is easy to underestimate demagogues, to make excuses for them, to try to co-opt them, to convince yourself that they are not as serious a threat as they appear, until it is too late. And I fear that this is what is happening with the resistible rise of Donald Trump.

What Trump and Hitler have in common is that they are both demagogues whose appeal is to base instincts of racism, xenophobia, and hatred. And they are both political outsiders, clever rhetoricians who know how to blame their supporters’ genuine woes on imagined and defenseless enemies. Their conviction that the politics and politicians they opposed were illegitimate found a large audience. They found ways to outfox and flummox the parties on the right, and Hitler came to power over a divided left.

All historical analogies have their limitations, and once again, Donald Trump is not Adolf Hitler. But it is time to take Donald Trump, and his presidential ambitions, very, very seriously. He has run the most nakedly racist significant campaign for president since George Wallace in 1968. He might well win the GOP nomination. He has been able to be as successful as he has, because his targets have been defenseless, undocumented Latinos and Muslim immigrants, and the famous statement by Pastor Niemöller—they came for the x’s, and I was not an x—has never been more apt. Indifference to high levels of deportation of Latinos under Obama, which has not become a major political issue, has greatly contributed to Trump’s success. I just hope a future generation of historians will not have to debate, as they do with Hitler, whether his plans evolved over time, or were set in his mind from the beginning.

Let me return to Kübler-Ross and her five stages. You can’t defeat death, but you can defeat demagogues. And the sixth stage, victory, can often be the saddest of all, when people realize that all of the death and destruction, all of the misery, could have been avoided if only they had paid enough attention, if they had been united, if they really empathized with the victims of the demagogue’s wrath before the demagogue was able to put his plans into action. This was a common reaction after the defeat of Hitler. I do not know what will happen over the next seven months, and I know this sounds alarmist. But it is time to sound the alarm. If America is not to be permanently stained by a Trump presidency, Americans will have to rise to the occasion.

Okay, Trump may not win the Republican nomination. But it certainly is possible. And it’s not that if Rubio wins the nomination things would be much better, but Rubio or any other Republican nominee is a much more conventional threat. American democracy is not nearly as rickety as that of Weimar Germany, but it is getting more brittle by the day, and a Trump presidency would place it under unprecedented strains. I don’t know if Trump will be able to expel the 11 million undocumented aliens from the United States, but we need to assume that he will make every effort to do so, and his efforts would find considerable Republican support. He will make every Muslim and Arab in this country, second-class citizens. And in doing so, we can expect him to challenge every restraint on his power, and expand the presidency to new imperial heights.

Let us hope for the best but prepare for the worst. Let us cry wolf rather than be devoured by one. Trump must be defeated in November. Democrats must unite behind a single candidate as soon as possible; they must support the candidate, if not with enthusiasm, at least whole-heartedly. We will need to recognize that if Trump is the candidate, regular partisan politics are over. The Democratic candidate will need to effectively reach out to independents, moderates, disaffected Republicans, all sources of potential anti-Trump votes. I hesitate to use the phrase the Communist Party used after 1933, but there needs to be a united front, a popular front, against Trumpism. We must be prepared for what will be a vicious campaign by a wily and resourceful campaigner; we must depict Trump as the evil force he is, and we are in for a close election. And if we win, we will have to work to scour Trumpism from our political life, and that will not be easy.