Donald Trump‘s first 100 days in office have left Britain in a difficult position on defence despite the UK-US “special relationship”, experts have suggested. In the weeks since Mr Trump returned to office he has upended the global order, sparking a trade war and signalling the White House’s security priorities lie outside Europe.

Despite the so-called “special relationship”, the UK has not escaped a 10% baseline tariff on goods entering the US. US Vice President JD Vance also sparked a row when he savaged Britain as a “random” country that he said hadn’t fought a war for decades. Mr Vance’s bombshell speech at the Munich Security Conference in February also pointed to a marked weakening of the transatlantic alliance which has persisted for decades. After just 100 days, the second Trump administration has left many in the UK asking how reliable the US will be as an ally outside the seemingly warm personal relationship between British Prime Minister Sir Keir Starmer and Mr Trump, who is due to enjoy an unprecedented second State Visit to the UK.

A key plank of the UK-US alliance has been the “special relationship” between the two countries, which is prized in London and has dominated UK foreign policy for years. It stems in part from a commitment from the United States to act as a guarantor of peace in Europe after World War 2. The UK and US have maintained deep defence, security and intelligence ties for decades since and share a nuclear agreement which leaves the UK reliant on US technology.

Dr Maria Ryan, an Associate Professor at the University of Nottingham who specialises in post-Cold War US foreign policy, said Britain would now be naïve to rely on an “outdated” idea of a “special relationship” with the US.

She told the Express that allies of the United States including the UK are now mulling their long term defence and security, adding the world may even be at the very beginning of a post-NATO world because the US security guarantee which has been at its heart since 1949 is “no longer trusted”.

Dr Ryan said countries will begin to make alternative arrangements, adding: “Nowhere will this transition be more difficult than the UK – because Britain does not want to lose its nuclear deterrent, which is heavily reliant on US tech and designs, or its access to US intelligence.”

She added: “This is not to say that the US and UK will not have a friendly relationship in the future, but British foreign policy will need to look beyond its relationship with the US. It is naïve to continue to rely on an outdated notion of a ‘special relationship’ with the US.”

The expert said that under President Joe Biden, US alliances with other countries helped to multiply the country’s ability to project power. She added: “The thing that makes Trump different to all other post-World War 2 presidents is that he doesn’t believe alliances enhance American power. He sees them as a drain on US resources. This is profoundly disruptive for all US allies.”

Angelia Wilson, Professor of Politics at Manchester University, said the “special relationship” won’t rupture under the Trump administration, but the president’s focus is firmly on the US.

She told the Express: “I would not rely on Trump being your best friend on defence at the moment. He’s not going to help if NATO steps up to protect Ukraine, for example.”

Professor Wilson said US guarantees to defend Ukraine wouldn’t be popular with most Americans or defence leaders and suggested that under Mr Trump the US wouldn’t rush to defend NATO allies or other countries, including the UK.

The expert said: “There is a particularly special relationship with the UK, but at this moment I would not want to bet on Trump coming to the UK’s defence. But if he were to come to any country’s defence, it would be the UK.”

She admitted the US and UK have been closer under President Ronald Reagan and former prime minister Margaret Thatcher as well as when Bill Clinton and Sir Tony Blair were leaders of the United States and Britain.

But Professor Wilson added: “Trump is very much focused on the US… The best anyone can hope for is not to be in the crosshairs of whoever Trump is aiming at on this particular day.”

While the “special relationship” has been tied to defence, security and intelligence, it has also been justified by shared values, though experts warn these too are being tested.

Steven Pincus, Thomas Donnelly Professor of History at the University of Chicago, told the Express Mr Trump has abandoned the “common ground” which united Winston Churchill, Franklin Delano Roosevelt (FDR) and even Joe Biden and Boris Johnson.

He said Churchill and FDR committed themselves to protecting governments which respected the rule of law and to reopening commercial ties between Britain and the US. The expert said the “special relationship” has “ebbed and flowed” since the wartime leaders made their commitment, but it has been “very strong”.

Professor Pincus added: “Even as Republicans alternated with Democrats in the US, and as Labour Prime Minsters replaced Tory ones, the fundamentals of the relationship remained strong. But at the moment the special relationship is strained in new ways.”

He said this has almost nothing to do with the personality or political preferences of Prime Minister Sir Keir Starmer. “Instead, it is Mr Trump who has abandoned America’s founding commitment to protecting countries that respect the rule of law in favour of more autocratic regimes like Hungary or Russia coupled with his insistence of abandoning basic principles of the free movement of goods that has frayed the relationship.

“By reversing America’s traditional foreign policy orientation and reimagining America’s economic principles Trump has abandoned the common ground that united Churchill and Roosevelt, Reagan and Thatcher, and even Joe Biden and Boris Johnson.”

Professor Ryan said attempts to justify the “special relationship” by emphasising the two countries’ shared values is now “hard to accept” given Mr Trump tried to overturn the results of the 2020 election and appears to be pursuing a social agenda many in the UK will consider regressive.

She added: “Trump believes in a world in which might is right and stronger powers can use coercion to achieve their goals – not good for a relatively small country like the UK…

“The popularity of Trump and ‘Trumpism’ calls into question the idea that a ‘special relationship’ based on shared values can be the basis of UK foreign policy.”