“No. 1, I am the least anti-Semitic person that you’ve ever seen in your entire life. No. 2, racism, the least racist person.” So the president said at a news conference in February. These words left me uneasy. A moment ago, as I was looking at photographs of young men in Charlottesville, Va., who were from my home state, Ohio, and thinking about the message “Heil Hitler” on the T-shirt that one wore, it dawned on me why.

I spent years studying the testimonies of Jewish survivors of the Holocaust and the recollections of their rescuers. When the rescuers were asked why they did what they did, they usually avoided the question. If they ventured a reply, it was simply to say that they did what anyone would have done. Historians who read sources develop intuitions about the material. The intuition I developed was that people who bragged about rescuing Jews had generally not done so; they were, in fact, more likely to be anti-Semites and racists. Rescuers almost never boast.

I write these lines in Poland, where the Holocaust is present in every absence, in a house where the Polish Nobel Prize-winning poet Czeslaw Milosz spent his summers when he was the same age as the young men I see in those photographs. In 1943 in Warsaw, he watched as the wind that blew the ash over the wall of the burning ghetto caught the skirts of girls riding a carousel. He noticed how people reached out to catch bits of ash floating through the air like “dark kites.”

I found myself thinking also of another Polish Nobel Prize-winning poet, Wislawa Szymborska. She memorably described a seemingly normal woman who was caught up in her daily cares but, when the moment arrived, ran headlong into a burning building to save children who were not her own.