In the year 1929, the Nazi propaganda tabloid Der Stürmer published a caricature of an imaginary group of devious looking Jewish people peeling off in a car after apparently running over a German boy, left bleeding in the arms of his father.

In the year 2017, the president of the United States retweeted a video of a dark-haired teenager assaulting a blond, Dutch teenager on crutches, with the erroneous caption, “Muslim migrant beats up Dutch boy on crutches!”

In the year 1942, the Nazi pamphlet Der Untermensch accused Jews of delighting in destroying churches, with the caption, “For the Jew and inhuman the highest satisfaction comes from the destruction of churches!”

In the year 2017, the president of the United States retweeted a video of a bearded Muslim man smashing a fair-skinned statue of the Virgin Mary with the caption, “Muslim Destroys a Statue of the Virgin Mary!”

For many Americans who woke up to President Trump’s tweets Wednesday morning, these videos seemed unduly hateful, and in the case of the video of the boy on the crutches, even fraudulent. (According to Dutch authorities, the assailant was born and raised in the Netherlands.) But for researchers of propaganda, the historical parallels within the videos were more chilling than anything else. There are, they say, just two differences between the German caricatures and the president’s tweets. First, the social media age has given Trump more readers on Twitter than Der Stürmer or Der Untermensch ever had. And second, we have no way of knowing how this chapter in history will end.

"I think this is real dangerous shit," says David Livingstone Smith, a professor of philosophy at the University of New England, who specializes in the history of dehumanization and who authored a book on the topic called Less Than Human.

"This is scary shit," echoes Jason Stanley, a professor at Yale and author of the book How Propaganda Works, whose father fled Nazi Germany in 1939.

To be clear and compliant with Godwin's law no one is comparing Trump to Adolf Hitler. "That would be absurd," Smith says. His concern is that the president and the general public have not learned history's lessons about the impact this type of fear-mongering can have. That's especially true today in the age of Facebook- and Twitter-driven echo chambers, in which any headline, photo, or video can be slyly captioned or edited to distort its original meaning to comply with a group's existing bias. The long past of propaganda blended with the communication channels of the present and future form a toxic mix.

"I think this is real dangerous shit." David Livingstone Smith, University of New England

Trump's tweets may look like an impulsive and offensive attempt to pander to the Ann Coulter wing of the Republican party, but looked at through the long lens of history, Trump's messaging has dangerous undertones that could be compared to propaganda tactics found in the well-worn playbook of how to demonize entire categories of humans. As forbidden as such historical comparisons are in polite society, Smith says, it's in ignoring history altogether that societies risk falling into the time-tested trap of believing that pending mass atrocities clearly announce themselves in bright neon lighting.

"There’s always a backstory," he says.

It typically begins with leaders fomenting fear, specifically by portraying a relatively powerless group as a societal threat. One of the most powerful examples of this was the portrayal of African American slaves in the antebellum south. "African Americans were the most vulnerable members of the population," Smith says, "Yet they were represented as violent monsters, particularly African American men, who were represented as almost super-human in the danger they posed."

The script repeated in 1934, one year after Adolf Hitler took power, when German Jews were already being herded into the Dachau concentration camp outside of Munich. The front page of Der Stürmer featured a headline, typed out in red and underlined, that read, "Jewish Murderplan Against Gentile Humanity Revealed."