Biarritz, France (CNN) This weekend, Boris Johnson is making his leadership debut as on the world stage at the G7 in the French resort of Biarritz.

It is a moment the UK Prime Minister has cherished since childhood. And, in the eyes of many Brits, he has gambled the UK's future to achieve it.

Since becoming PM, Johnson has had one goal: to get the UK out of the European Union, a message he has hammered home this week in meetings with France's President Emmanuel Macron and German Chancellor Angela Merkel.

In Biarritz, he will also meet with US President Donald Trump, Japan's Shinzo Abe, and Canada's Justin Trudeau. Johnson's moment in the sun will come when, if as expected, he and Trump unveil their much-hyped steps to a post-Brexit trade deal.

It will be a handy trophy of sorts, which is intended to dazzle British voters and convince them that, despite the advice of the government's own civil servants and experts, Brexit will benefit the British economy.

All of which will soon be hugely important as Johnson faces a looming challenge to his leadership and a general election.

While Brexit is the talk of diplomats and business leaders the world over, little mention is being made of his apparent bet on America, the presidency of Trump, and all that entails.

To side with America rather than the EU, as Johnson has been showing recently, risks committing the UK to far more than Brexit.

Johnson is a risk-taker: while his gamble on Trump might benefit him today, it also risks breaking Britain, splitting the four-nation Union, and potentially putting it on the wrong side of emerging geopolitical fault lines.

The reasons are relatively straightforward: the world has changed a lot since the Brexit vote in 2016.

Indeed it is a very different place than it was when former prime minister David Cameron promised a referendum on EU membership in 2013.

However while the world has moved on, Euroskeptics have not.

Photos: British Prime Minister Boris Johnson Britain's new Prime Minister, Boris Johnson, waves from the steps of No. 10 Downing Street after giving a statement in London on July 24. Hide Caption 1 of 29 Photos: British Prime Minister Boris Johnson A 21-year-old Johnson speaks with Greek Minister for Culture Melina Mercouri in June 1986. Johnson at the time was president of the Oxford Union, a prestigious student society. Hide Caption 2 of 29 Photos: British Prime Minister Boris Johnson Johnson started his career as a journalist. He was fired from an early job at The Times for fabricating a quote. He later became a Brussels correspondent and then an assistant editor for The Daily Telegraph. From 1994 to 2005, he was editor of the weekly magazine The Spectator. Hide Caption 3 of 29 Photos: British Prime Minister Boris Johnson In 2001, Johnson was elected as a member of Parliament. He won the seat in Henley for the Conservative Party. Hide Caption 4 of 29 Photos: British Prime Minister Boris Johnson Johnson looks apologetic after fouling Germany's Maurizio Gaudino during a charity soccer match in Reading, England, in May 2006. Hide Caption 5 of 29 Photos: British Prime Minister Boris Johnson Johnson is congratulated by Conservative Party leader David Cameron, right, after being elected mayor of London in May 2008. Cameron later became prime minister. Hide Caption 6 of 29 Photos: British Prime Minister Boris Johnson Johnson, left, poses with a wax figure of himself at Madame Tussauds in London in May 2009. Hide Caption 7 of 29 Photos: British Prime Minister Boris Johnson Johnson poses for a photo in London in April 2011. He was re-elected as the city's mayor in 2012. Hide Caption 8 of 29 Photos: British Prime Minister Boris Johnson Johnson and his wife, Marina, enjoy the atmosphere in London ahead of the Olympic opening ceremony in July 2012. The couple separated in 2018 after 25 years of marriage. Hide Caption 9 of 29 Photos: British Prime Minister Boris Johnson Johnson gets stuck on a zip line during an event in London's Victoria Park in August 2012. Hide Caption 10 of 29 Photos: British Prime Minister Boris Johnson Johnson poses with his father, Stanley, and his siblings, Rachel and Jo, at the launch of his new book in October 2014. Stanley Johnson was once a member of the European Parliament. Hide Caption 11 of 29 Photos: British Prime Minister Boris Johnson Johnson takes part in a charity tug-of-war with British military personnel in October 2015. Hide Caption 12 of 29 Photos: British Prime Minister Boris Johnson Johnson kisses a wild salmon while visiting a fish market in London in June 2016. A month earlier, he stepped down as mayor but remained a member of Parliament for Uxbridge and South Ruislip. Hide Caption 13 of 29 Photos: British Prime Minister Boris Johnson Johnson arrives at a news conference in London in June 2016. During the Brexit referendum that year, he was under immense pressure from Prime Minister Cameron to back the Remain campaign. But he broke ranks and backed Brexit at the last minute. Hide Caption 14 of 29 Photos: British Prime Minister Boris Johnson Johnson sits next to Prime Minister Theresa May during a Cabinet meeting in November 2016. Johnson was May's foreign secretary for two years before resigning over her handling of Brexit. Hide Caption 15 of 29 Photos: British Prime Minister Boris Johnson As foreign secretary. Johnson meets with US House Speaker Paul Ryan in April 2017. Johnson was born in New York City to British parents and once held dual citizenship. But he renounced his US citizenship in 2016. Hide Caption 16 of 29 Photos: British Prime Minister Boris Johnson Johnson launches his Conservative Party leadership campaign in June 2019. Hide Caption 17 of 29 Photos: British Prime Minister Boris Johnson Johnson and Foreign Secretary Jeremy Hunt take part in the Conservative Leadership debate in June 2019. Hide Caption 18 of 29 Photos: British Prime Minister Boris Johnson Johnson speaks in July 2019 after he won the party leadership vote to become Britain's next prime minister. Hide Caption 19 of 29 Photos: British Prime Minister Boris Johnson Britain's Queen Elizabeth II welcomes Johnson at Buckingham Palace, where she invited him to become Prime Minister and form a new government. Hide Caption 20 of 29 Photos: British Prime Minister Boris Johnson Johnson poses with his dog Dilyn as he leaves a polling station in London in December 2019. Hide Caption 21 of 29 Photos: British Prime Minister Boris Johnson Johnson appears on stage alongside Bobby Smith during the count declaration in London in December 2019. Johnson's Conservative Party won a majority in the UK's general election, securing his position as Prime Minister. Hide Caption 22 of 29 Photos: British Prime Minister Boris Johnson Johnson and his partner, Carrie Symonds, react to election results from his study at No. 10 Downing Street. Hide Caption 23 of 29 Photos: British Prime Minister Boris Johnson Johnson speaks on the phone with Queen Elizabeth II in March 2020. Hide Caption 24 of 29 Photos: British Prime Minister Boris Johnson In March 2020, Johnson announced in a video posted to Twitter that he tested positive for the novel coronavirus. "Over the last 24 hours, I have developed mild symptoms and tested positive for coronavirus. I am now self-isolating, but I will continue to lead the government's response via video conference as we fight this virus. Together we will beat this," Johnson said. He was later hospitalized after his symptoms had "worsened," according to his office. Hide Caption 25 of 29 Photos: British Prime Minister Boris Johnson After recovering from the coronavirus, Johnson returned to work in late April 2020. Hide Caption 26 of 29 Photos: British Prime Minister Boris Johnson Johnson wears a face mask as he visits the headquarters of the London Ambulance Service NHS Trust in July 2020. Hide Caption 27 of 29 Photos: British Prime Minister Boris Johnson US Secretary of State Mike Pompeo sits across from Johnson in the garden of No. 10 Downing Street in July 2020. Hide Caption 28 of 29 Photos: British Prime Minister Boris Johnson Johnson holds a crab in Stromness Harbour during a visit to Scotland in July 2020. Hide Caption 29 of 29

Clash of the titans

Trump won the US presidential election a few months after Brexit and has subsequently shown that America is not the reliable ally it once was.

He has picked fights with friends, Germany, Canada, France, and even the UK, while mollycoddling dictators like North Korea's Kim Jong Un. This week, in an extraordinary move even by his own unpredictable standards, he dissed Denmark, dumping out of an upcoming state visit, deeming it no longer worthwhile because it won't sell him Greenland.

Trump is utterly undependable, but it is in the case of China that he most threatens the post-Brexit calculus.

The Asian superpower is coming of age, inevitably challenging the United States. China believes its technology sector should have a fair shake at dominating and appears willing to endure a bitter trade war with Trump to achieve it.

A clash of these titans is on the horizon, and neither can be relied on to act in a way that might have been imagined five years ago.

If Johnson wants a taste of what this could ultimately look like, he needs to look beyond the uplifting platitudes of fast trade deals with the US that Trump's national security adviser, John Bolton, promised during his visit to London earlier this month

Betting the bank on US

If Johnson looks to Hong Kong and listens to the threats thrown at the UK by Beijing, he won't hear anything remotely friendly. Any wish to have a fruitful trade deal with China is exactly that -- a wish.

China is on the way up and, thanks to Trump's trade war, the world is heading for an us-versus-them universe.

There will be two camps, pro-America; pro-China, and Johnson appears to be betting the bank on America.

The recent clashes over Chinese technology firm Huawei was a harbinger of issues that lie ahead.

Bolton's trip to London and Johnson's apparent backtracking on allowing the Chinese tech giant to build part pf the UK's 5G network is one of several signals that the UK is tilting towards Trump.

The week before he took office, Jeremy Hunt, the UK's former foreign secretary, said Britain would look to EU allies to provide security for British tankers under threat in the Persian Gulf.

Hours into office, Johnson turfed Hunt out of the job and gave it to his hardline Brexiteer colleague, Dominic Raab.

Raab has wasted little time reversing Hunt's words, thrusting Britain into America's willing arms to help it -- not following the EU lead in securing shipping in the important oil transit waters just off the coast of Iran.

It's what America wants, and so, it seems, does Johnson, despite Gibraltar, a UK overseas territory, refusing to accede to US demands to hand over an Iranian oil tanker temporarily impounded there.

He has succeeded in convincing the country and the EU he'll leave the 28 nation alliance on 31st of October, "do or die."

Bolton says America will support the UK. Of course he did -- Trump wants the EU to be as weak as possible.

But it's worth asking the question, is Johnson siding with America simply to make the EU take his no-deal threat more seriously? Or is he really throwing the UK's lot in with America.

Then-UK foreign secretary Boris Johnson met President Trump at the UN headquarters in September 2017.

Out in the cold

If the latter, where does that leave the UK, post-Brexit?

While the EU is far from homogeneous in its view of Trump's America -- Poland, Hungary and some of Italy's leaders are big fans -- Germany and France fear his protectionist anti-EU policies.

In China's eyes, the EU may look less like an economic threat than America. Any EU nation will be able to maintain an ambiguous relationship, warm and fuzzy with Trump if they like, but when dealing with China benefiting from the collective bargaining power that the EU brings to trade deals.

Should Johnson deliver Brexit, the UK would be out in the cold and at the mercy of an unpredictable US President than might seem to be the case as Johnson bigs up his time with Trump at the G7.

Johnson would do well to look at the legacy of another prime minister, Tony Blair. Blair was popular and had a huge majority (which Johnson does not) until he got caught up in former US President George W. Bush's 2003 Iraq war.

Blair lasted 10 years, five of them after the invasion of Iraq. If Johnson gets his gamble wrong, 10 months in office could seem like a stretch, leaving the UK paying the price long after he is forgotten.