In February of 2016, after winning the New Hampshire primary, Sen. Bernie Sanders gave a speech in which he identified himself as “the son of a Polish immigrant.” This was not exactly false—Sanders’ father, Eli, did come to America from Poland, at the age of 17. But it wasn’t exactly true, either, since as many Jews hastened to point out, a Jew from Poland is not and never was simply Polish. On the contrary: From the 14th century, when large numbers of Jews began to settle in Poland at the invitation of Casimir the Great, until 1939, when the Holocaust killed 90 percent of the country’s 3.5 million Jews, it was clear to Jews and Poles alike that they were two very different peoples who happened to share the same piece of territory. They could be neighbors and business partners, but they were seldom friends and almost never relatives or social or legal equals. It is only the amnesia of American Jews that allows us to blur a line that was, historically, blindingly bright.But it is not just American Jews who have trouble making sense of the place of Poland in the Jewish story. Today almost every Ashkenazi Jewish community in the world has roots in Poland (though the geography of historic Poland overlaps only partly with its current political borders). It was in the late 19th century that the Jews of Poland—which was then not a sovereign state, but a territory divided among the Russian, Austrian, and Prussian crowns—began to surge out by the millions, driven by poverty and heightened persecution. This means that the Jews of all countries are only four or so generations removed from Poland; it is the mother of us all, but a cruel mother, one we are glad of having escaped. When the descendants of Irish or Italian—or Polish—emigrants go to visit the Old Country, they find relatives and ancestral villages. When Jews go to Poland, there is little for them to see, except Auschwitz.Yet it is the very elusiveness of the Polish Jewish past that makes the need to understand it so compelling. This is as true for Ivan Jablonka, author of A History of the Grandparents I Never Had, as it is for Agata Tuszyńska, author of Family History of Fear. The lives of these writers have been very different. Jablonka is French, a professor of history at the University of Paris, while Tuszyńska, a poet and biographer, was raised in Warsaw, the daughter of a Catholic father and a Jewish mother. The former is far removed from Poland, geographically and culturally, while the latter still lives within miles of her ancestors’ homes. Yet for both, the journey to the past covers vast mental and emotional distances. Making that journey means swimming against the tide of forgetting—not just the ordinary forgetting that makes everyone’s ancestors vague and somewhat foreign, but the deliberate erasure that was inflicted on the Jews of Europe in the Holocaust.For Agata Tuszyńska, who was born in the 1950s, that erasure took the form of concealment. It was not until she was 19 years old, she writes, that her mother Halina revealed that she had been born Jewish. In America today this kind of concealment might seem bizarre. But in Communist Poland, Tuszyńska says, it was entirely understandable: “She didn’t want to weigh me down with a burden heavier than I could bear. She didn’t want her child to have to grow up with a feeling of injustice and fear.”Indeed, one of the themes of Family History of Fear is that fear of anti-Semitism is a rational emotion in Poland even today. In one of the book’s most staggering moments, Tuszyńska tracks down the Polish family that sheltered her mother as a young girl during the Holocaust. The son of that family, now an old man, remembers the little Jewish girl who came to live with them: “She used to take the cows to pasture, and she slept there in the next room.” Then he bursts out: “What was the use of doing all that? Why did my mother put her whole family at risk? Why all that? What are they doing to us now? It’s a shame and a disgrace how the Jews have dominated the whole world. I don’t know why we had to save them.”To be a “righteous gentile,” Jews today might naively assume, must be a badge of honor, a cause for pride. For this Pole, however, it was a stupid mistake, a case of being duped by Jewish guile. And he’s not the only person we meet in Family History of Fear who feels that way. When Tuszyńska visits the small town of Łęczyca, where her ancestors originated, she meets a blacksmith who explains to her that the Jews who used to live there committed ritual murder, draining the blood of Polish children to make matzoh. “These aren’t just empty stories,” he assures her. In a nearby town, someone has painted a slogan on a wall: “The Jews are looting this country.” One might think that Polish anti-Semites could look around them with satisfaction: A country that once had three-and-a-half-million Jews now has 20,000. But the hatred outlives its object. Like a phantom limb, the missing Jews of Poland continue to haunt the body politic.But, of course, this is far from the whole story. For it is a Pole, a history teacher named Mirek, who guards the records of the Jews of Łęczyca and who helped Tuszyńska find traces of her ancestors there. “Freeing himself from this widespread prejudice that had gone on for years required the courage of an independent thinker,” she observes. And during the war, it was a Pole who rescued many of Tuszyńska’s relatives, including her mother, from the Warsaw Ghetto. This was Alexander “Oleś” Majewski, her Aunt Frania’s Catholic husband, a bigamist and womanizer who seemed to have no great affection for Jews in principle yet risked his life to smuggle his wife’s family over to the “Aryan side” of the occupied city. “Without Oleś … there would be no trace of any of us,” Tuszyńska writes. “I would never have come into this world because my mother and her mother … would never have gotten out of the ghetto.” Still, she observes that, growing up, she never noticed her Jewish relatives showing Oleś any particular warmth. “Had they forgotten what he did for them? … They accepted being saved by the hands of Oleś, and after some time they considered it normal. Offered. It didn’t require eternal gratitude.”Another kind of ambiguity haunts the marriage of Tuszyńska’s parents. Her mother, Halina, met her father, Bogdan, when the two were journalism students at the University of Warsaw in the early 1950s. Halina was unmistakably Jewish—though she had been baptized after the war, as a safety measure—and Bogdan was classically Polish, blond and blue-eyed. But they were united by their faith in Communism, which they believed was going to build a new, just society, transcending the differences of the past. Clearly, Bogdan was no Jew-hater. Yet Tuszyńska recalls that, throughout her childhood, her father was given to making anti-Semitic remarks: “To him, Jews were the reason, vague but ubiquitous, for everything that didn’t go as it was supposed to. … He held them responsible for every unpopular law, for whatever problems he currently had at work, for the scarcity of new tires for his automobile.”“I did not understand what any of that meant,” Tuszyńska writes. “I had never met a Jew.” Except, of course, for her own mother, whose Jewishness was still a secret. As always happens with family secrets, however, the young girl could tell that something was missing, hidden, awry. “The feeling of being worse than the others remained superficial, but I never managed to figure out where it came from,” she writes. “I had to work hard to be better than others. It was really important, and a lot of things depended on it.” Indeed, to her mother, their very lives must have seemed to depend on being the best Polish citizens they could be—which meant, at the time, the best Communists they could be.In addition to telling Tuszyńska’s own family story, Family History of Fear is also a book about the bitterly ironic relationship between Jews and Communism. For some Jews in under Czarist rule, in the early 20th century, Communism looked like the solution to the poverty and prejudice that plagued them. To be a Communist was to transcend Jewishness, to render it meaningless—which is why Jewish Communists proved to be among the fiercest enemies of Jewish religion and culture. Yet while only a tiny percentage of Jews were Communists, enough visible Communist leaders were Jews to cement the identification in the minds of many Poles. This helped to fuel Polish anti-Semitism during the Holocaust; and when Communism came to power after the war, Jews paid for their improved legal and social status with the resentment of much of the population.Eventually, the hatred prevailed, and in 1968 an anti-Semitic campaign—couched, not for the last time, in the language of anti-Zionism—drove out most of what remained of Poland’s Jewish community. In Family History of Fear, we see this tragic dynamic unfold in the life of Tuszyńska’s maternal grandfather, Samuel. He survived World War II because he had been an officer in the Polish army and was taken prisoner by the Germans in September 1939. This meant that he was kept miserably alive in a POW camp rather than being exterminated as a Jew. After the war, Samuel rose to a high position in the government office responsible for rebuilding the devastated city of Warsaw, and he gave the Communist Party his gratitude and allegiance. But in 1968, he was forced out of his job by the anti-Semitic tidal wave. Friends stopped speaking to him, and one day he found his doorknob covered in feces. Communism had not abolished anti-Semitism in Poland; instead, it created new forms and new excuses.***For Tuszyńska, the hopes of Jewish Communists died in 1968. For Ivan Jablonka, on the other hand, the Jewish romance with Communism still has something exciting and noble about it today. He is gratified to find that “the grandparents [he] never had,” Mates and Idesa Jablonka, grew up in interwar Poland as committed Communists—so much so that both did time in Polish jails as political prisoners. “These modern-day Prometheans were seeking to break with the status quo and unleash the blessing of freedom in all its forms,” he writes. Things didn’t work out that way, of course; even in the 1930s, when Mates and Idesa were hanging banners and distributing leaflets, informed observers of the Soviet Union knew that Communism was the opposite of “freedom.” But Jablonka, like many Jews, admires the idealism of his Communist forebears. “It would be an illusion to think that their aspirations were an illusion,” he writes, even as he acknowledges that Mates’ “freedom and his voice were being poisoned by totalitarianism.”Jablonka is a professional historian, and one of the pleasures of his book is that it demonstrates the historian’s craft in action. Starting in 2007, he conceived the idea of writing about Mates and Idesa, who were killed in the Holocaust when their son Marcel, Jablonka’s father, was a young child. He knew little about their story when he began, only that they had made their way from Poland to France in the late 1930s and that they had been deported from Paris to Auschwitz during the Nazi occupation. Yet he discovers that even the most anonymous lives leave traces—in the case of his grandparents, a surprising number of traces because they had so many encounters with government bureaucracies. To start with, there are records of Mates’ trial and imprisonment in Poland in 1933. Ironically, the crime that landed him in jail was not trying to overthrow the government, but planning an attack on the local Zionist party. (There has always been a ferocious enmity between Jewish nationalists and Jewish universalists.)After Mates and Idesa came to France as illegal immigrants in 1937, there are records of their run-ins with the immigration system, which repeatedly tried to expel them, but without success. In 1939, archives show that Mates enlisted in the French Foreign Legion, hoping to fight Hitler and gain French citizenship. Using memoirs and published histories, Jablonka traces the career of his grandfather’s regiment, an outfit made up mostly of Jewish and Spanish refugees with no military training. They were hurled into the front line during the brief, disastrous German invasion in 1940 and then demobilized after the fall of France.Fatefully, Mates returned to Paris, in the Occupied Zone, where his wife and children were waiting. Jablonka uses census data to find out the names of all the inhabitants of the tenement where they lived and then uses phone directories to track down their descendants. In this way, he is able to draw up an almost room-by-room description of the building where Mates and Idesa spent their last months. And by consulting police records, he is able to at least hypothesize about the sequence of events that led to the couple’s arrest, early in the morning of Feb. 25, 1943. His own father, three-year-old Marcel, escaped; he and his older sister Suzanne were sent to a neighbor’s apartment every night, in case of just such a pre-dawn raid. This neighbor, a Catholic Pole, hid the children from the police and handed them over to family friends, who in turn entrusted them to a French couple named Courtoux in Brittany. Just like Tuszyńska, Jablonka is alive today only because of the heroic actions of righteous gentiles, who risked their own lives to save Jews.One might think that Jablonka’s research could take him right up to the gates of Auschwitz but no further. Surely the death camp is a black hole where no light can penetrate. But in fact, he is able to construct a remarkably full portrait of exactly what befell Mates and Idesa after they were deported. Thanks to the meticulous record-keeping of the Nazis, he knows exactly which transport they were on and when they arrived at Auschwitz. Just when Idesa died is uncertain, but a chance encounter with a survivor after the war allowed the family to learn that Mates survived the initial selection on the ramps and that he was assigned to the most horrifying job in the camp: He was a Sonderkommando, charged with operating the gas chambers and crematoria.This is the kind of knowledge that a grandson, even a historian like Jablonka, might be happier not to possess. “Living in the past, this past, in particular, can drive one around the bend,” he admits. Even with all the facts he has discovered about his grandparents, the truth about them—what they were really like, what they thought and felt and suffered—remains forever hidden. “The sum of all our acts does not reveal who we are, and a few randomly collected ones reveal nothing at all,” he writes near the end of the book. But Jablonska and Tuszyńska testify to the fact that even this “nothing” is precious. When people—when a people—have suffered so deep a loss, they are grateful for any confirmation that their past really existed. It is a way of reminding themselves of what they must sometimes doubt: that they, too, are real.