THE exclusion of the BBC, together with leading United States news organisations, from a White House press briefing may seem a small matter. So may President Donald Trump’s announcement that he is to boycott the White House correspondents’ annual dinner, at which every US President since 1924 has been the guest of honour.

But we should all be concerned that the leader of the foremost military superpower repeatedly brands as a peddler of “fake news” and an “enemy of the people” any journalist who dares to criticise or even question him.

Alarm bells should ring at the phrase “enemy of the people”, which has been used by repressive regimes throughout history, from the French Revolution to Soviet Stalinism. It was a favourite device of the Nazi propaganda minister, Joseph Goebbels.

The internet meme Godwin’s Law insists that you lose any argument once you are reduced to drawing a parallel with Hitler and the Nazis. But this wry observation on worldwide web wildness seems less funny than it did with the arrival of President Trump.

Last week, I suggested that President Trump’s persistent blurring of the line between fact and fiction, and his preference for ideological opinion over empirical truth, was not stupid, but sinister (Comment, 24 February). It is the modern equivalent of the propaganda technique known as “The Big Lie” — the telling of untruths so “colossal” that few would believe that anyone “could have the impudence to distort the truth so infamously”. The quotation comes from the man who formulated the notion in 1925. It is in Chapter 10 of Adolf Hitler’s Mein Kampf.

Hitler, another man who bluffed his way into power via the ballot box, suggests that “the great majority of a nation is so feminine in its character and outlook that its thought and conduct are ruled by sentiment rather than by sober reasoning.” To manipulate this, “all effective propaganda must be confined to a few bare essentials,” constantly repeated “in stereotyped formulas”. President Trump’s ex-wife, Ivana, disclosed during their divorce that her husband kept a book of Hitler’s collected speeches, My New Order, in his bedside cabinet.

Hitler left the details to Goebbels, who, early on, launched a systematic assault on the independence of newspapers. One technique was to single out a particular “enemy” for special vilification. For Goebbels, it was The Munich Post, which was eventually closed, and many of its journalists disappeared or were sent to Dachau. Attacks on The New York Times by President Trump’s cronies thus have sobering echoes.

Of course, Godwin’s Law is correct in advocating caution. There are many areas in which parallels between Nazi Germany and Trumpist America do not hold. For all President Trump’s alarmist rhetoric, the US economy is in pretty good shape, unlike that of Weimar Germany; and the checks and balances of the US constitution are robust, as judicial challenges to the Muslim travel ban have shown.

But an independent press is vital to an effective democracy. It scrutinises the actions of the executive and holds it to account. Wilful attempts to undermine this are alarming. All the world should be troubled.