In the almost 20 years since we moved our three young children from a bucolic street in West Los Angeles to a Jerusalem apartment in the rough-and-tumble Middle East, my wife and I consciously taught them that in going from the United States to Israel, we had not been fleeing anything. We had moved not from something but to something. The country in which they were born, we reminded them time and again, not only was the greatest democracy on the planet (after which Israel largely models itself) but also has been unique in Jewish history. Everywhere else, Jews had lived tenuously, doing their best to be accepted until their host community eventually tired of them. When that happened — as in England in 1290, Spain in 1492 and Germany in 1933 — horror ensued.

America, even in its occasional ugly moments, was fundamentally different. Yes, many Americans harbored no love for Jews. But the country’s proud self-image as a nation of immigrants and, more important, the rights guaranteed in its revolutionary Constitution, usually demanded that they more or less keep that to themselves. Growing up in Baltimore in the 1960s and 1970s, I experienced not a single instance of blatant anti-Semitism. True, there was that day in Manhattan when an enormous guy suddenly blocked my way and yelled, at the top of his lungs, “Jew!” When I periodically find myself at the corner of Madison Avenue and 54th Street I still relive that memory. But it lasts for a moment and I immediately move on. Jew-hatred in America seemed no laughing matter, but I was never worried about the future of Jews in America.

Then came Donald Trump and a series of “missteps” that added up to something deeply ominous. There was the refusal to distance himself from David Duke. And the Holocaust Remembrance Day speech in which Mr. Trump neglected to mention Jews. There was the campaign ad against Hillary Clinton, with a background of a Jewish star and images of money. Steve Bannon and the alt-right got increasing access. At some rallies, his supporters shouted, “Hail Trump.” It wasn’t “Heil Trump,” but in front of our eyes, more quickly than we ever feared, America was transforming.

Throughout the campaign, though, our now thoroughly Israeli adult children refused to worry. We had taught them that America was different. And they had grown up in a country the very purpose of which was to eradicate Jewish fear. Max Nordau, a Zionist ideologue and contemporary of Theodor Herzl, wrote about the need for “Muskeljuden,” or “muscular Jews,” who would put victimhood behind them. Zeev Jabotinsky, a contemporary of Mr. Herzl and Mr. Nordau, argued that if Jews had any hope of succeeding in their sovereign aspirations, they would have to be an “Iron Wall” — they would have to make their enemies understand that attacking Jews never ended well for the attackers. In myriad ways, the Jewish State was about eradicating diaspora Jewish fear.