Britain was said by the great Victorian historian JR Seeley “to have conquered and peopled half the world in a fit of absence of mind”. The US is losing its global power in the same way.

Through ignorance and malice, Donald Trump is destroying the foundations of US influence that previous leaders spent three-quarters of a century erecting. When it comes to “soft power”, he is engaging in unilateral disarmament – and that in turn will have dire consequences for US security and prosperity.

Trump is entirely focused on US hard power – military and economic might. An administration official described his worldview as follows: “His dream would be to have a strong military that protects our homeland. We’d wall ourselves off and strike at our discretion and then retreat to defending our homeland.” This was not a viable policy even in the early 20th century; it certainly won’t work in the 21st century in a world that has been brought more closely together by communications and transportation technologies.

What Trump doesn’t realise is that much of the country’s success as a superpower has rested on its “soft power”. The US is a superpower by invitation: it has troops in more than 170 countries and alliances with at least 60 countries because most other nations do not feel threatened by US power.

Anti-Americanism is a fact of life, but the US simply has not engendered the same kind of fear and loathing that less altruistic, more militaristic would-be hegemons have done – notably, Habsburg Spain, monarchist and Napoleonic France, Wilhelmine and Nazi Germany, and the Soviet Union. Each of those superpowers provoked other nations to ally against its expansionist designs, eventually leading to its downfall.

There is no similar international coalition against the United States because it has widely been viewed as a more benign actor. In the past, its adversaries – China and Russia – were the isolated ones. These illiberal powers have a few satraps but almost no real friends. They are regarded with suspicion and hostility by their neighbors. But now Trump’s unilateralism is leaving an opening for these illiberal states to usurp US power.

While clashing with democratic leaders … Trump has gotten along disturbingly well with dictators

Trump has abandoned not only the Trans-Pacific Partnership but also the Paris climate accord and the Iran nuclear deal. He then impulsively accepted a summit meeting with the North Korean dictator, Kim Jong-un, before just as impulsively abandoning it – and then moving to reinstate it after all. These are indications of how the administration “grownups” cannot contain his unilateralist (and erratic) instincts for long.

Trump’s words speak volumes about his contemptuous attitude toward allies. During his first year in office, he had testy exchanges with, among others, the prime minister of Australia and the president of Mexico.

Not even the US’s closest ally was safe from Trump’s criticisms. In June 2017, after a terrorist attack in London, Trump blasted that city’s first Muslim mayor, Sadiq Khan, tweeting: “At least 7 dead and 48 wounded in terror attack and Mayor of London says there is ‘no reason to be alarmed!’” Trump misrepresented the mayor’s remarks – Khan had said there was no need to be alarmed about a heightened police presence on the streets, not about terrorism.

A few months later, in November 2017, the prime minister, Theresa May, rebuked Trump for posting anti-Muslim videos produced by a far-right British group. Trump instantly hit back, lecturing the prime minister: “Don’t focus on me, focus on the destructive Radical Islamic Terrorism that is taking place within the United Kingdom. We are doing just fine!”

Facebook Twitter Pinterest ‘Trump’s relationship with the chancellor of Germany was just as testy as with the prime minister of the United Kingdom.’ Photograph: Leon Neal/Getty Images

Trump’s relationship with the chancellor of Germany was just as testy as with the prime minister of the United Kingdom. It is perhaps no coincidence that the leaders of both countries are intelligent, strong-willed women. With the notable exception of his daughter, Ivanka, Trump does not appear comfortable dealing with independent women. During the 2016 campaign, Trump bashed Angela Merkel for admitting Muslim refugees into Germany. “I think what she did in Germany is a disgrace,” he said, adding that he was no longer “a fan”. When the two leaders met at the White House in early 2017, Trump pointedly refused to shake Merkel’s hand. Then in May, following a G7 summit in Italy where Trump clashed with the European leaders over the Paris climate accord, Merkel emerged to say that Europe could no longer count on the US. “We Europeans truly have to take our fate into our own hands,” she declared.

Just about the only democratic leaders with whom Trump developed cordial relationships were Shinzo Abe of Japan and Emmanuel Macron of France – the former because he played golf with Trump (and probably let the American win), the latter because he took Trump to a military parade in Paris. But not even the budding Abe-Trump bromance could spare Japan from being included on the list of nations subject to Trump’s ill-advised steel and aluminium sanctions, and Macron could not prevent Trump from pulling out of the Iran nuclear deal.

While clashing with democratic leaders – especially those who happen to be women or minorities – Trump has gotten along disturbingly well with dictators. He positively purred after the Saudis in May 2017 projected a five-storey-high photo of him on to the side of his hotel in Riyadh. In July 2017, Trump had a tête-à-tête with Vladimir Putin at the G-20 summit in Hamburg that began with the American president telling the Russian autocrat what an “honor” it was to see him. In November 2017, Trump was even more laudatory after a visit with Xi Jinping in Beijing.

He said that his feeling toward Xi was “an incredibly warm one”, and described Xi as a “highly respected and powerful representative of his people”. Correction: Xi is not the “representative” of his people. He is their dictator, and it’s impossible to know how respected he is because anyone who is disrespectful to him is likely to be locked up. Xi is currently orchestrating the most intense cult of personality that China has seen since the days of Mao Zedong – and Trump is doing his level best to help. He declared that it’s “great” that Xi was making himself president for life and added, supposedly in jest, “maybe we’ll have to give that a shot some day”.

Facebook Twitter Pinterest ‘He said that his feeling toward Xi was “an incredibly warm one”, and described Xi as a “highly respected and powerful representative of his people”.’ Photograph: Nicolas Asfouri/AFP/Getty Images

Trump has a kind word for every strongman he chats with. He congratulated Rodrigo Duterte of the Philippines because “of the unbelievable job” he was doing “on the drug problem” – a problem that Duterte is addressing by unleashing death squads that have killed thousands of Filipinos. He said that Recep Tayyip Erdoğan was “getting very high marks” as he was crushing civil society and congratulated him on a rigged referendum that spelled the death knell for Turkish democracy. He said that Egypt’s Abdel Fattah al-Sisi, who has jailed thousands of Islamist and liberal dissenters, had “done a fantastic job in a very difficult situation”.

All US presidents have been forced to deal with dictators. Recall Franklin Roosevelt’s apocryphal aphorism about Anastasio Somoza García of Nicaragua: “He may be a son of a bitch, but he’s our son of a bitch.” But no president has been so greasy and fulsome in his blandishments. For Trump, these dictators’ attacks on democratic norms are not a problem but rather policies to be praised – and possibly even emulated.

For years, as a seller of real estate and star of reality TV, Trump made a living wooing, if not bamboozling, customers and viewers. Yet, once in office Trump has proved to be the worst salesman that the US has ever had. Far from winning over other countries, he is actively repelling and repulsing them.

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According to Gallup, “approval of US leadership across 134 countries and areas stands at a new low of 30%”. That’s lower than the 34% approval during the last year of George W Bush’s administration in the wake of fiascos such as the Iraq war. Even more ominously, the number of Arab youths who see the US as an enemy shot from 32% in 2016 to 57% in 2018. After Trump pulled out of the Iran nuclear accord over the objections of the Europeans, Donald Tusk, president of the European commission, tweeted: “Looking at latest decisions of @realdonaldtrump someone could even think: with friends like that who needs enemies.”

American power had been eroding even before Trump came to office, thanks to the growth of competitors such as China and the foreign policy mistakes of George W Bush, who was too interventionist, and Barack Obama, who was too non-interventionist. Trump has accelerated the decline. He might even have made it irreversible. What ally will trust America ever again? Even if a future president reverts to a more internationalist and free-trade policy, the rest of the world will be acutely conscious of the risk that the American electorate might choose another isolationist and protectionist president in the future. Trump may well be ending the Pax Americana and helping to usher in either a Chinese century or a new global disorder where there is no international law and life is “nasty, brutish and short”.