In the late ’30s my parents, like all Germans, were required to go to city hall to prove they were pure Aryans. Since nobody in my family aspired to higher office, they had it relatively easy. They needed only “The Lesser Aryan Certificate,” which required seven birth or baptism certificates (their own, their parents’, and their grandparents’), plus three marriage certificates (again their own, their parents’, and grandparents’). However, anybody who sought higher office had to prove Aryan heritage dating back to 1750. This early on, people with as little as one-eighth of Jewish blood were ostracized. I asked my mother why she didn’t refuse this ordeal, and she told me she would not have been allowed to continue her apprenticeship as a kindergarten teacher. My father would not have been permitted to own and operate his beloved toy store any longer. We all know how this division between Aryans and the “racially impure” played out.

I’ve spent my whole life wondering how such unspeakable evil could have happened in Germany, an enlightened democracy with a rich cultural tradition and a pluralistic society. In college I studied fascism, researching and writing papers about the many theories seeking to explain the nature and rise of the Nazis in Weimar Germany. Neither historians nor psychologists could provide satisfactory explanations for evil on such a staggering scale.

Neither could my relatives who experienced Hitler’s rise and the ensuing war first-hand. Other than one grandmother, they all claimed not to have wanted, or voted for, Hitler. And what exactly should they have done about it anyway? Any opposition would have landed them in a camp, or at the very least in some unpleasant trouble.

Right now, so long after I had resigned myself to the notion that I will never understand how a Hitler and the Holocaust could have happened, I’m seeing how it is possible for a dangerous demagogue to come to power. And it terrifies me.

Donald Trump has been compared to Adolf Hitler numerous times. Even though the political and economic circumstances in the U.S. today differ vastly from those in Weimar Germany in the ’30s, the similarities in the rise of these two demagogues, especially their xenophobic rhetoric, are impossible to deny. Trump claims Mexico is sending waves of drug dealers and rapists across the border. And so, if elected president, he has promised to build a wall to keep Mexicans out—even though more Mexicans are leaving the U.S. than coming in. He says he will not allow Muslims to enter the U.S. and will require all resident Muslims to carry ID cards identifying them as Muslims, information that will be entered into a national database. In Nazi Germany, Jews’ passports were all stamped with a capital J, and the yellow Star of David had to be visible on all Jews’ clothing. Should Trump’s vision come to pass, Muslims might want to hide their religion. Will there be a mandatory trip to city hall for everyone in America to prove they’re not Muslims? ...