In its outward details, the orderly transfer of American presidential power accomplished in the inauguration-day scene on Capitol Hill today felt time-honoured. The ceremonial essentials of the occasion – the stars and stripes banners, the dignitaries and the prescribed rituals of the swearings-in – were familiar and traditional. Political rivals took their places on the podium as they do every four years, shook hands and applauded one another, offering gracious compliments and providing a show of national dignity.

Yet all this was in fact a sham. Donald Trump’s inaugural address was a declaration of war on everything represented by these choreographed civilities. President Trump – it’s time to begin to get used to those jarringly ill-fitting words – did not conjure a deathless phrase for the day. His words will not lodge in the brain in any of the various uplifting ways that the likes of Lincoln, Roosevelt, Kennedy or Reagan once achieved. But the new president’s message could not have been clearer. He came to shatter the veneer of unity and continuity represented by the peaceful handover. And he may have succeeded. In 1933, Roosevelt challenged the world to overcome fear. In 2017, Mr Trump told the world to be very afraid.

Mr Trump’s speech was by turns bitter, blowhard and banal. It boiled with resentment and contempt for politics, and the checks and balances of the US system. It was aimed at those who voted for him, not at those, the majority, who did not. It said barely a word about race. Its America First nationalism was crude and shameless. The speech seethed with scorn for everything about the capital city that he now seeks to bend to his will. It was, though, almost wholly empty of detail or of clarity about how its goals would be achieved. Even before he opened his mouth, Washington was on edge about what a Trump presidency might mean and the world was on edge about what is happening to America. Everything Mr Trump said confirmed that those instincts were correct. Presidents have often come into office promising to take the nation on a new path. But if Mr Trump can be believed, his election and his speech signal the biggest shake-up in Washington in living memory.

The vital question for the future is whether Mr Trump can be believed. In his speech he mocked those who have been all talk and no action. But there is a risk he could be a victim of that too. He raised the bar for his own presidency to a very high level by insisting that everything would change “right here, right now”. But will it? The power of the presidency has grown over the decades, and the 2016 election has now put the Republicans in charge of all the arms of government. But Mr Trump is not, at least not yet, a dictator. He has to govern with a Congress that does not share all his priorities – in some cases, Mr Trump’s priorities may even be preferable – and according to law that is interpreted by the courts. The states have a lot of power to defy him, as California seems determined to do in the case of the planned wall with Mexico.

It has been argued that voters chose Mr Trump knowing that he would challenge the system, but confident that the system would protect the voters from the worst consequences. That may prove right. But Mr Trump should not be underestimated. He is a proud disrupter not a diffident conformist. He is – and intends to be – different from the presidents of the past: in his personality, his working style, his ways of communicating and, most important of all, in his political aims. Those who support him and those who fear him are agreed on that. Yet he has arrived in the White House with low ratings and amid a deep sense of division. His inauguration was boycotted by several leaders and will be protested against by tens of thousands. His attempts to overturn America’s political hierarchy and culture will enthuse some – the stock market is thrumming – but terrify others.

The realities of Mr Trump’s disruptive intentions will be revealed in the weeks and months ahead. The first downpayments on his turbulent agenda can be found on the White House website. Domestically, the biggest programme will be the infrastructure projects that formed the only detailed pledge of the inaugural address. Beyond America’s shores, much is still guesswork: the probable clash with China poses the biggest threat of all; whether Mr Trump gets his way on Russia may depend on his more sceptical cabinet.

“The time for empty talk is over,” said President Trump today. “Now arrives the hour of action.” At home and abroad, and in the light of today’s speech, that is a truly terrifying prospect.