Eighty-five years ago on Thursday, Heinrich Himmler opened the Nazi’s first concentration camp at Dachau. History does not repeat itself. But it is laced with warnings.

Since the Holocaust, anti-Semitism has been the west’s largest taboo. Today it is creeping back from the fringes. Its return is most remarkable in the US and Britain. Everyone should take note. When the strongest taboo cracks, lesser ones may crumble.

In the 1930s, fascists railed against “rootless cosmopolitans”. Today’s version of the latter are “globalists”. Anti-Semitism channels hatred of modernity. The biggest spur to this in the US is the Donald Trump effect. According to the Anti-Defamation League, anti-Semitic incidents in America rose by nearly 60 per cent in 2017 — by far the largest jump since it began monitoring. Whether Mr Trump stokes it unwittingly is an open question. That he has had a big impact is undeniable. How else to explain a near doubling of anti-Semitic incidents in US schools in his first year in office? Children mimic grown-ups. Society takes its cues from leaders.