The word from the White House is that the events at Charlottesville are behind them now, and they’re ready to move on. Sure, there is still some fallout from the 12 August march by neo-Nazis, white supremacists and the Ku Klux Klan, as well as from Donald Trump’s subsequent declaration that those racists and fascists who carried flaming torches and swastika flags included some “very fine people”. There are reverberations too from the president’s initial non-condemnation condemnation, in which if he saw “hatred, bigotry and violence” at all, he saw it “on many sides”.

Berlin police tighten security for neo-Nazi march after Charlottesville attack Read more

One such aftershock came today, when Gary Cohn, Trump’s chief economic adviser, told the Financial Times the administration “must do better” in denouncing such groups unequivocally, and that, “as a Jewish-American”, he had considered resignation. Still, the message from Team Trump is that all this is in the past. They want the focus to switch to the legislative battles ahead, especially to their plan to give a gargantuan tax cut to the richest people and corporations in America.

They might just get away with it. One of the dizzying lessons of this presidency is that outrage can be dulled by outrage, that fury at one atrocious act is hard to sustain if fury at another soon replaces it. Consider that only four weeks ago Trump all but called for police brutality, telling an audience of uniformed officers they had no need to treat suspects gently. Or that a week or so later he took the world to the brink of nuclear confrontation with North Korea. There is a numbing effect to the frequency of such horrors. We become punch-drunk.

But if Trump succeeds in moving past Charlottesville, it won’t only be thanks to an unavoidable process of attrition that has worn liberals down. I’m afraid Trump’s opponents made a tactical error. He wanted to change the subject to the question of Confederate statues – and they let him. Days after those violent clashes had seen an antiracist protester murdered, the national conversation centred not on that act of terrorism but on which historical figures should be remembered, and how.

Make no mistake, that’s an important argument. But it is inevitably a nuanced one that, as we have seen in Britain too, divides liberal opinion. Two people, equally fervent in their loathing of racism, might disagree on whether it’s better to remove a monument, or keep it as a reminder of a shaming past. And there will never be an easy consensus on where to draw the line. If owning slaves is the key criterion, should the statues of George Washington and Thomas Jefferson come down too?

Play Video 2:27 President condemns violence 'on many sides' – video

Trump’s opponents have spent much of the past two weeks talking about Confederate generals and US history, when they should have maintained a laser focus on the key and shocking point: that an American president spoke with sympathy and admiration for neo-Nazis; that he put these fascists on a moral par with those who oppose them; and that he was more animated in condemning what he called the alt-left than he ever was in lambasting those who parroted the slogans of the KKK, who brandished the symbols of white supremacism and who chanted: “Jews will not replace us.”

These are the key facts that should shock every American and a watching world. And here’s what’s at stake.

For 70 years, since the end of the second world war, a consensus held across the democratic world that seemed so obvious it barely needed stating. It declared that some ideas are beyond the pale, that certain beliefs are taboo because they are unconscionable.

The key prohibition was on any ideology whose organising principle was genocidal racism. It meant, therefore, that even to use a phrase or image associated with the Nazi credo ensured instant ostracism: think of the periodic controversies over public figures accused of dressing up in Nazi regalia, replicating the “sieg heil” salute, or using the phrase “final solution”. Whatever else we might disagree on, all but a tiny, isolated fringe understood and accepted that Hitlerism was out of bounds.

Drunken American beaten up for giving Nazi salute in Germany Read more

Incredibly, Trump has ditched that understanding. When he praised those marchers, he stomped all over that taboo. What’s more, and crucially, he has done it without paying a price. Cohn may have agonised privately, as perhaps have some other Trump aides. (It’s barely worth mentioning Trump’s son-in-law, Jared Kushner, who the novelists Michael Chabon and Ayelet Waldman predict will be remembered as one of the Jewish people’s “greatest traitors and greatest fools”.) But not one of them has resigned. A few Republicans have rebuked him. But the collective repudiation of Trump that this act surely merited has not come.

It is this non-reaction that announces that the Nazi taboo is dead. Now it’s clear that it can be broken without consequence, it has lost its force. Indeed, the effect of Trump’s action is to have opened up the veins of the US, allowing the poison of the far right to flow into the bloodstream. A poll taken after Charlottesville found that 9% of Americans believe holding neo-Nazi or white supremacist views is acceptable. That’s 30 million people.

It never used to be this way. When the KKK burned a cross on the lawn of a black home in Maryland in 1982, Ronald and Nancy Reagan visited the Butler family to reassure them that the racists did not represent America. And now the man sitting in Reagan’s chair praises those who wear the Klan’s robes as “very fine people”.

All this is a cue for Trump’s opponents to redouble their efforts to bring this horrific presidency to an end. But it is also a warning against our own complacency.

We may have believed that the tacit prohibition on Nazi ideas was sufficiently entrenched that it no longer needed defending. The history is taught in schools, and replayed in endless TV documentaries. But when almost one in 10 Americans see no problem in the ideology of a movement that killed tens of millions – and that sought the total eradication of a specific group, namely Jews, from the face of the earth – then the task is clear.

We need to teach the darkest chapter in human history with renewed vigour, as if for the first time. And we have to do it with the urgent understanding that this is no longer about the past – but about averting a deadly future.