In 2012, Barack Obama made an uncharacteristic gaffe that set off a small diplomatic crisis - he referred to the "Polish" - and not "Nazi" - death camps of the Second World War.
For Poles, it was an acutely painful faux-pas. The nation has for years objected to the term "Polish death camps", saying it implies complicity in the Nazi camps built on its soil during occupation.
President Obama swiftly apologised, and a personal letter to Poland's then president Bronislaw Komorowski was enough in that case to paper over the diplomatic crack.
But under a bill passed by Poland's lower house of parliament this week, someone using similar language in future might be prosecuted. Put forward by the ruling right-wing Law and Justice Party, the bill would make it a crime to accuse Poland of being complicit in the Holocaust, punishable by up to three years in prison.
President Andrzej Duda has indicated he will likely sign it into law. "There was no participation by Poland or the Polish people as a nation in the Holocaust," he said on Monday.
There is widespread agreement among historians that some Polish citizens did participate in the Holocaust, by betraying, even murdering Polish Jews. But there is disagreement over whether those acts add up to wider Polish complicity — a nuanced historical debate that the Polish government now seeks to legislate.
"This is history as a tool, as a means for a nationalistic government to accuse everyone else of betraying the nation while painting itself as the only true carriers of the Polish flag," said Anita Prazmowska, a professor of Polish history at the London School of Economics (LSE). "It is a blunt instrument."
It is also a product of the current political moment in Poland, where 60,000 nationalists took to the streets in November to denounce Islam and immigration, and where historians see a once progressive post-Soviet state taking a dark turn towards right-wing populism.
For years after the war, under communism, talk of complicity was effectively silenced in Poland, from the left and the right. The Communist Party had no interest in being seen as the defenders of Jews; right-wing nationalists had no desire to wash Poland's dirty laundry in public.
But the stories were there, carried by witnesses, rescuers, and survivors — a complex history of heroic actions, terrible betrayals and even massacres.
When the Nazis seized the Polish border town of Piotrkow in 1939, nine-year-old Ben Helfgott was forced into a ghetto alongside his family. When the SS first attempted to transport him to a camp in 1942, he was saved by a Polish manager at the glass factory where he worked, who told the SS that he was not a Jew.
"It was not easy for Poles to help at that time, they risked their own lives," said Mr Helfgott, now 88, from his home in England.
He was eventually transported to Buchenwald in 1944, aged 14, and ended up in the Theresienstadt camp where he was liberated in 1945. The horror wasn't over though — when he returned to Piotrkow he was racially abused and nearly murdered by Polish army officers.
"I was saved by a Pole and I was nearly killed by a Pole. That is my history, it cannot be changed," he said. "They can pass a law but it cannot work. Many people, Jews and Poles, have written about this history. It is there in books. You cannot change it."
It was a book that finally forced Poland, in 2000, to reckon with the darker chapters of its past. Neighbours, by historian Jan Gross, told the story of a 1941 pogrom in the village of Jedwabne, where at least 340 Jews were locked in a barn and burned alive by their Polish neighbours. The account was based on interviews with witnesses, murderers, and survivors, and it shocked the country out of a long period of denial.
"Jan Gross threw a hand grenade into the debate," said Ms Prazmowska.
Other historians followed. In 2013, Professor Jan Grabowski concluded that at least 200,000 Jews who escaped the liquidation of the Polish ghettoes were killed, directly or indirectly, by Polish citizens. His book, Hunt for the Jews, detailed a complex history of inducements and threats by Nazis and moral compromises by Poles.
"For years these topics had been off the table. There was a consensus of silence that was broken by Jan Gross," said Mr Grabowski.
The years after Mr Gross's book were characterised by a sense of moral and cultural renewal for Polish historians, said Dr Joanna Michlic of the Centre for Collective Violence, Holocaust and Genocide studies at UCL - a sense that national honour could be found in a truthful interrogation of history.
That flame of renewal is guttering under Poland's new nationalist government, she said. The Law and Justice Party, elected in 2015, has made it clear that it sees statements of Polish complicity as a stain on the country, and now potentially a criminal offence.
"The saddest thing is that these kind of policies are against the rescuers and the Holocaust survivors," Dr Michlic said. "Those people who witnessed terrible events in their own communities, what will happen to them, will they be taken to court over their own stories?"
Zigi Shipper was sent to Auschwitz aged 14, from the Lodz ghetto in Poland. "Many Poles risked everything to save Jewish lives, but there was also the opposite, there were people who gave their neighbours away," said Mr Shipper, now 88. "There were good ones and bad ones, and people should be free to tell those stories."
The bill was condemned by Holocaust charities as well as the US, EU and by Israel, which offered to foot the legal bill of anyone charged. The Polish prime minister, Mateusz Morawiecki defended its intentions, saying that Poland would "never limit the freedom to debate the Holocaust". The Law and Justice Party, president's office, and the Ministry of Justice did not respond to requests for comment.
The bill does contain a clause that would, in theory, exempt "artistic or academic activity" from prosecution. But historians who spoke to the BBC were sceptical about the protections it would offer.
"The question is, who decides?" said Dr Michlic. "Who decides what is art and what is historical study? ... And what about the teachers and the journalists and the witnesses? On paper they are not exempt."
According to an Associated Press report, the passage of the bill through parliament was followed by a surge of anti-Semitism online and in Polish state media.
Some of that anti-Semitism ends up in Mr Grabowski's mailbox. In the past it was sent anonymously, he said. Now it is signed, and it includes threats against his family.
With that shift, "you do not even need a law on the books", he said. "Imagine you are a PhD student, do you really want to cross an unwritten line, when your career depends on funding from the state?"
Even a simple interview between an academic and a journalist might violate the new law, he said.
"This is not an academic pursuit, there is no exemption here. I could go to jail for this interview I give you and you could go to jail as a journalist. You see? You are complicit too."