In his book “How to Get Rich,” published in 2004, Donald Trump made a confession. “I have to admit that my knowledge of classical music is limited,” the now US president said.

That seems kind of ironic given that the desire to call the tune has always been the Trump way. This weekend as the G20 summit draws to a close, Trump however, has been far from the one calling the tune.

As the current leader of the G20, the German chancellor Angela Merkel, got to choose the music for the customary summit concert that took place on Friday night, when some of the most powerful men and women in the world swapped the conference room for the concert hall after the day’s intense negotiations.

Ludwig van Beethoven’s Ninth Symphony was Merkel’s choice, though the piece’s final movement, better known as the “Ode to Joy” - the official Anthem of Europe - was well out of key with the prevailing mood in Hamburg.

As political leaders arrived for the Beethoven concert in the Elbphilharmonie concert hall on one side of the river, protesters blared the music of Jimi Hendrix from the other side.

Earlier as meetings between leaders of the club of 20 largest global economies wrapped up on Friday, police stormed the last holdouts of anti-capitalist protesters who have taken to the streets in an effort to disrupt the city’s gathering of global leaders.

Heavily armed police commandos eventually moved in after activists had spent much of the day attempting to wrest control of Hamburg’s streets from more than 15,000 police officers, setting fires, looting and building barricades.

If the mood in Hamburg’s Schanzenviertel district, an area known for its left-wing activism and culture of squatting, was at times ugly, it was sometimes little better behind the scenes of the summit, where political wrangling over everything from climate change to trade was the order of the day.

Critics have often dubbed the G20 the world’s largest and most ineffectual international organisation, but this year’s meeting had an unusually added tinge of edginess in that it also involved the first face-to-face meeting between Donald Trump and Russian president Vladimir Putin. The encounter was one of the most eagerly anticipated meetings between two leaders in years.

As the real estate tycoon and the former spy shook hands, political and diplomatic observers scrutinised the coming together in an effort to determine who would come off best from the summit.

Sir Malcolm Rifkind, the former British foreign secretary, likened the event to “two alpha males prowling around one another”, admitting the potential outcome kept him awake at night.

“It is a huge problem that Putin cannot predict how Trump is going to behave,” he said, adding: “That is because Trump does not know how he is going to behave.”

In the event, the meeting ran longer than either side had planned, Trump and Putin discussed alleged Russian meddling in the US election but agreed to focus on better ties rather than litigating the past.

According to US Secretary of State, Rex Tillerson, Trump had “positive chemistry” with Putin during the meeting, which lasted for over two hours.

“The presidents rightly focused on how do we move forward from what may be simply an intractable disagreement at this point,” Tillerson insisted. That explanation did not sit well with US Democrats.

“Working to compromise the integrity of our election process cannot and should not be an area where ‘agree to disagree’ is an acceptable conclusion,” countered US Senate Democratic leader Chuck Schumer in a statement.

Some US observers have pointed to the fact that despite what Tillerson described as “very robust” and “very constructive” discussion, Americans and others are no closer to getting a straight answer from Trump as to what role, exactly, he thinks Russia played in the 2016 US presidential election. What has emerged from the meeting however, is that Putin and Trump bonded over their hostility towards a free press and that another ceasefire was brokered over Syria.

According to Tillerson, what also surfaced from the meeting between the two leaders was that both countries have more in common than what separates them. These areas of common ground though do not appear to include Ukraine, North Korea’s nuclear programme, or the US deployment of the Terminal High Altitude Area Defence (THAAD) missile defence system to South Korea, which Russia has said should stop, and which apparently did not come up in the two-hour-and-15-minute meeting.

Before the get-together, some feared Trump a political novice whose team is still developing its Russia policy, would be less prepared for the talks than Putin, a former KGB agent who has dealt with previous US presidents and scores of other world leaders.

These concerns were only compounded when US National Security Adviser, H.R. McMaster admitted that the US administration had “no specific agenda” for the meeting.

But while the Trump-Putin encounter remained at the public epicentre of the summit, the wider focus of attention centred on whether this might be the moment that would bring about the US’s formal abdication as the world’s pre-eminent power.

This potential reshuffling in terms of global power was aptly captured in what some dubbed the annual ‘family photo’ of the world leaders.

G20 protocol dictates that those who have been in office the longest occupy the centre positions, the only exception being the host nation, whose leader – in this case Angela Merkel - gets the prime slot.

Trump, who became US president less than seven months ago, found himself positioned near the end of the first row, with only French prime minister Emmanuel Macron to his outside.

Merkel, who is gearing up for a parliamentary election in September, has aimed at cementing Germany’s growing global leadership role with a demonstration of its unwavering commitment to free speech, assembly and dissent by holding the summit in the centre of Hamburg, a city with a proud radical tradition.

The German leader however has faced the daunting task over the last few days of steering the G20 toward a consensus on trade, climate change and migration, all issues that have become more contentious since Trump entered the White House half a year ago promising an “America First” approach.

Last month he pulled the United States out of the Paris Accord, the landmark international agreement aimed at combating climate change. Trump has also threatened to take punitive trade measures in the steel sector that would hit China, Germany, Canada and a host of other countries. Such moves have pitted Trump against virtually every other country in the club of leading economies.

“The sherpas have a lot of work ahead of them tonight,” Merkel said late Friday, referring to the trade dossier. “I hope they can bring us a good result tonight. But here the discussions are very difficult, I don’t want to talk around that.”

As if such issues were not problem enough, the summit is also taking place against a wider backdrop of substantial international turmoil.

Over the past week tensions have risen over North Korea where another missile test indicated a further step forward for Pyongyang’s ambition to successfully deliver a nuclear weapon.

There are serious problems too in the Gulf, where since last month four Arab countries - Saudi Arabia, the United Arab Emirates, Egypt and Bahrain - have cut diplomatic ties and severed air, land and sea links with Qatar.

The bloc has now issued an ultimatum to a 13-point list of demands that included cutting ties with terrorist groups, curbing relations with Iran and shutting media outlets including Al-Jazeera.

So just precisely at the moment when international tensions are flaring, the G20 finds itself pondering whether they should still look to the US for global leadership.

Increasingly, though, there is a sense that the moment has arrived whereby Washington’s leadership role has waned to the point that it will be passed not to a single successor, but to a new unstable quartet of Donald Trump, Xi Jinping, Vladmir Putin and Angela Merkel.

As the protocol surrounding the G20 ‘family photo’ suggests there is significant symbolism to the US president being on the outer reaches of world leaders, particularly when a year ago Barack Obama was front and centre next to Merkel.

For some time now there have been significant signs of this shift in terms of international diplomacy and cooperation.

At its heart lies Trump’s insistence in embracing a set of “America First” policies that put the values of international cooperation firmly on the backburner.

Most notably, he pulled the United States out of the Paris climate accord, making the US only the third country not signed up to the historic agreement to tackle climate change.

In his speech announcing the decision, Trump encapsulated his approach by plainly stating that he represents the people of “Pittsburgh, not Paris.”

Predictably, the decision was met by widespread condemnation around the world, notably by Macron and Merkel.

Following Trump’s first visit to Europe, during which he failed to pledge the United States’ commitment to NATO’s Article 5, the principle of common defence, Merkel said that the era of Europe being able to fully rely on the US was over under Trump’s leadership.

Some American commentators now concur with Merkel’s view. Derek Chollet who served in the Obama administration for six years and is now co-editor of Shadow Government, a blog about US foreign policy in the age of Trump, believes that the President has reduced America to the role of a “back-row kid.”

“During our time in the Obama administration, ‘How will America help fix this?', was a common refrain, one we heard over and over from our foreign counterparts about global problems,” says Chollet who is now convinced that refrain has all but been silenced.

“They believed in American “soft power”, the ability to set the agenda, bring others to the table, draw up a game plan, and take the lead in implementing that plan,” says Chollet of other nations.

Where once other powers saw America as the leader on a broad range of issues, from combatting terrorism to combatting climate change, Chollet now believes that role has been considerably diminished and lost direction under Trump.

“As a president, Trump leads by insult, intimidation, bluster, and boast. His policies are deeply troubling in many areas, whether it is pulling out of international agreements, threatening trade wars, or slashing the budget for diplomacy or development,” observed Chollet.

If the G20 has done nothing else, it has further exposed this seismic shift in America’s global standing. Rather that pulling the world’s major economies together, the gathering has served only to underline differences with the US.

The expectations from G20 summits are almost always low, but so little has this one achieved that some have rebranded the G20 the G Zero. Just before the summit started last week, one Russian media observer writing in the newspaper Rossiyskaya Gazeta pointed out that: “The main thing is that nothing gets worse.”

But worse it has got, largely due to the fact that Donald Trump does not believe in the idea that countries can achieve more by cooperating together.

Trump has long made it clear he does not buy the basic principles underlying the post-war world order. On one issue after another, the US has proven itself at odds with its G20 partners. It has become a simple case of America versus the rest. The refrains of Beethoven’s “Ode to Joy,” and its message as a hymn to humanity, peace and international understanding appear to have fallen on deaf ears when it comes to the US president.