The inauguration of a US president is normally a moment of great hope. It is a celebration of representative democracy and the peaceful transfer of power. It is an affirmation that the ideals and laws set out in the 1787 US constitution, still a global paradigm for modern-day governance, continue to be honoured and observed. Inauguration confers legitimacy on a head of state in the name of “we, the people”. The incumbent has a duty to respect and uphold the constitution’s central aims, namely “to form a more perfect union, establish justice, ensure domestic tranquillity, provide for the common defence, promote the general welfare, and secure the blessings of liberty”.

The inauguration this Friday of Donald Trump as 45th US president is not a normal moment. Nor for the majority of Americans who did not vote for him, and countless onlookers around the globe, is it a moment of hope. Rather, Trump’s ascent to what is commonly termed the world’s most powerful job is a moment of dread, anxiety and great foreboding. We said, after he won the Republican nomination last summer, that Trump has shown himself unfit to be president. His often-demonstrated ignorance, racial bigotry, misogyny, untruthfulness, hostility to free speech, crude bullying and dangerous, rabble-rousing nationalism utterly disqualify him.

Nothing has occurred since Trump narrowly won last November’s election, despite polling nearly three million fewer votes than the Democrats’ Hillary Clinton, to alter this unhappy conclusion. The president-elect’s press conference last week failed to justify hopes that the imminent, awesome responsibilities of office would moderate his reckless behaviour. In a matter of minutes, he slandered America’s intelligence agencies, threatened Mexico, vowed again to build a border wall, pistol-whipped US businesses that invest abroad, took a wrecking ball to Obamacare, pilloried unfavoured news organisations, and boasted about a shady $2bn business deal. This is not the behaviour of a president.

Although only days away from the Oval Office, Trump continues to blurt out half-baked opinions on sensitive issues, like a bar-room boor. He appears not to think before he opens his mouth or his Twitter account. And what pops out is usually offensive, inflammatory or inaccurate, exemplified by last week’s insulting of Meryl Streep. Hopefully, speechwriters more sensible than he will craft his inaugural address. Friday’s ceremony is a momentous occasion. It will be watched around the world. It is a showcase for America. Yet Trump is an embarrassment. His elevation is a national humiliation.

Few will enjoy this gross spectacle more than Vladimir Putin, Russia’s messianic president, and his plausibly deniable teams of cyberhackers, conspirators, fake newsmen and skilled muddiers of pools. Russia’s election interference on Trump’s behalf, publicly certified by the Obama administration and all the US intelligence agencies, has cast a dark shadow. The release last week of an unverified dossier alleging Russian contacts with Trump’s campaign staff and the gathering of blackmail material against him has intensified fears that Moscow is still trying, directly or indirectly, to manipulate the president-elect, by exploiting his inexperience, vanity and naive view of Putin.

Trump has flatly denied the dossier’s allegations in his customary, choleric way. But his narcissism, when combined with his visceral hatred of Barack Obama’s foreign policy and his susceptibility to flattery, makes him a vulnerable target. Putin calmly repudiated the dossier, refusing to be drawn into the dispute, just as he refused to react to Obama’s expulsion of Russian diplomats over the election scandal. Russia’s leader is plainly expecting political payback in the form of an early summit with Trump. Only then may his real objectives become clear, including perhaps the lifting of US sanctions over Ukraine, acquiescence in Russia’s annexation of Crimea, a free hand in Syria and a Nato pullback in eastern Europe. Meanwhile, Putin can sit back and enjoy the unprecedented confusion and disarray in Washington that his covert activities helped engender.

Yet for much of the confusion attending the transition, Trump alone is to blame. He often stresses his experience as a business leader and decision-maker. But decisive leadership has been alarmingly lacking amid the conflicting policy approaches promoted by his most senior nominees. Rex Tillerson, the ExxonMobil oilman improbably tapped for secretary of state, said last week the US would, in effect, besiege fortified islands Beijing has illegally created in the South China Sea. There is no doubt that the islands are a problem. But threatening to expel the Chinese by military force is not a sensible way to address it. This latest provocation follows Trump’s incendiary, off-the-cuff comments about Taiwan. Little wonder Chinese state media are warning of a coming war with the US.

The impression that Trump and his top advisers have little idea what they are doing and scant grasp of key issues has strengthened, rather than receded, as the transition has chaotically unravelled. Trump says the CIA are behaving like Nazis. Mike Pompeo, his nominee for CIA director, lavishes praise on the agency and pledges to investigate the same dossier that Trump dismissed out of hand. While Trump’s sons, acolytes and lawyers insist their billionaire daddy-boss will avoid conflicts of interest, Ben Carson, his choice as housing tsar, refuses to rule out the possibility of millions of dollars in federal grants benefitting Trump’s real estate empire.

A former general, James Mattis, slated to become defence secretary, revealed even bigger contradictions. Far from endorsing Trump’s ideas about enhanced future collaboration with Russia, Mattis identified Putin as a powerful foe intent on destroying Nato. It was vital, he said, that “we recognise the reality of what we [are dealing] with with Mr Putin”. Russia had chosen the role of strategic adversary and the US must be prepared to confront it. Mattis also declared Russian forces had committed war crimes in Syria, a view shared by the Obama administration, Britain and the UN, but one that has not been endorsed by Trump. Add to that Tillerson’s separate comments that Russia should be punished for “invading” Crimea and policy towards Moscow looks more than merely confused. As with China, it looks like Trump is spoiling for a fight.

Well, is he? The fact is, nobody knows – and that includes a lazy, muddled and largely clueless Trump himself. Spouting prejudices, selling slogans and making it up as you go along may work on the campaign trail. But it will not do in the White House.

Even if all Trump’s numerous inadequacies and sordid personal baggage were set to one side, his egregious lack of coherent, fact-based, rational and cooperative policy platforms, especially internationally, is potentially disastrous. Look again at what the US constitution demands: justice, tranquillity, liberty, common defence and the common good. All these principles are in peril. As the Trump era begins, a more imperfect disunion is the dismal prospect.