As George W Bush’s speechwriter put it this weekend, it is one of the “difficult but primary duties” of a political leader to speak for a nation in traumatic times. A space shuttle explodes, a school student goes on a shooting spree, a terrorist flies a plane into a building, a hurricane floods a city. When such things happen, Michael Gerson wrote in the Washington Post, “It falls to the president to express something of the nation’s soul.” Yet if Donald Trump’s words about the violent white extremist mobilisation in Virginia on Saturday – which an under-pressure White House was desperately trying to clarify on Sunday – are an expression of its soul, America may be on the road to perdition.

The original United States of America was built on white supremacy. The US constitution of 1787 treated black slaves as equivalent to three-fifths of a free white and gave no rights at all to Native Americans, who were regarded as belonging to their own nations. After the civil war, Jim Crow laws enforced segregation across the defeated south and comprehensively disfranchised African Americans for nearly a century. Writing Mein Kampf in the 1920s, Adolf Hitler praised America’s institutional racism as a model from which Nazi Germany could learn. Only in the postwar period, and then slowly and incompletely, was meaningful racial equality pursued by the land of the free.

Yet, while American racism has extremely deep and tenacious historical roots, without which the events in Virginia on Saturday cannot be properly understood, some large things have changed for the better over the past 60 or so years. Equal rights have been enforced. Equality has been embraced. America has elected a black president. It would be difficult to imagine any US president of this more recent period, of whatever party, who would not have responded to the neo-Nazis and white supremacists in Charlottesville with anything except explicit condemnation and disgust. Any president, that is, until this one.

There is absolutely no moral equivalence between the fanatical white supremacists who rallied in the Virginia city on Saturday and the equality defenders who demonstrated peacefully against them, one of whom was rammed and killed by a speeding car allegedly driven by a man who had attended the neo-Nazi rally. The supremacists hate black people and Jews, and regard white people as superior. They talk portentously about blood, soil and the right to bear arms. They admire Hitler and give Nazi salutes. They fly the flags of the pro-slavery Confederacy – the ostensible cause of their rallies this summer is Charlottesville’s decision, more than 150 years after the south’s surrender, to remove a statue of Robert E Lee from a park. And one of them committed the sort of act that was rightly called terrorism when it occurred in Nice, Berlin and London.

Yet, in his first response on Saturday, Mr Trump utterly failed in his primary duty to uphold equality and speak the truth about the racist violence that had taken place. Instead of placing the blame where it belonged, on the supremacists and Klansmen who triggered these events, and rather than stand up for the indivisibility of equality and tolerance before the law, Mr Trump’s words were by turns slippery, banal and morally compromised. It was not true that the violence in Charlottesville came from “many sides”, as Mr Trump evasively said, before repeating his evasion. It is the head of state’s duty to stand up, explicitly and unequivocally, against racists and those who promote racial violence. Mr Trump was found wanting.

That would not have happened under Mr Bush, for all his faults. Nor is it true of top Republicans like Cory Gardner, Ted Cruz, Marco Rubio and Orrin Hatch, none of them social liberals, who were all quick to call the supremacists out. Even the Senate majority leader, Mitch McConnell, who is few people’s idea of an ideological exemplar, condemned the racists. But Mr Trump did not.

It is hard to believe that the omission was an oversight and hard to treat it merely as a reminder of Mr Trump’s inadequacy for the presidency. The concern is that Mr Trump’s blathering was wholly deliberate until the White House got worried by the reaction. The worry is that he recognises that his election has empowered angry white people, including those who describe themselves as “alt-right” but who should be called what they are – white supremacists. The hope is that this dishonest and morally shaming moment will define Mr Trump for sufficient decent Americans that he will not be trusted again. Sadly, the evidence of modern America gives too few grounds for optimism.