Members of the Trump administration, on the eve of Prime Minister Starmer’s visit to Washington, are livid over a deal negotiated last year by Sir Keir to transfer Britain’s sovereignty over the Chagos island group to Mauritius, an ally of Communist China. An American-British military base at, Diego Garcia, an atoll in the islands, hosts one of America’s top submarine bases. The issue could rival that of Ukraine.

“I’m hopeful that President Trump will sink this deal as a threat to U.S. national security,” a former aide to Prime Minister Thatcher, Niles Gardiner, tells the Sun, adding that Mr. Trump’s opposition could mean a “game over” for Mr. Starmer’s deal. His deal  would transfer British sovereignty over the prized group of islands to Mauritius, “a country that is an increasingly close ally of Communist China,” Mr. Gardiner says.

“There’s no guarantee, whatever the wording of any agreement is with Mauritius, that Diego Garcia is going to be protected,” Mr. Gardiner adds.

On the eve of his Thursday White House visit, Mr. Starmer announced today that by 2027 Britain would raise its defense costs to 2.5 percent of its national domestic product, from the current 2.3 percent. Mr. Trump has long demanded that Europe increase its defense budgets. Mr. Starmer vowed to send peacekeeping troops to Ukraine following the end of the war there. 

Diego Garcia, though, has served America and Britain for a long time as a military hub in the Indian Ocean. The countries have utilized the bases there during the Iraq war, the struggle to defeat ISIS, and numerous other military skirmishes in the region. 

In 2019 the United Nations’s judicial arm, the International Court of Justice, ruled that Britain’s 1965 “separation” of the Chagos Archipelago from Mauritius was unlawful, violating international law and the right to self-determination. The United Kingdom, it ruled, must end “as rapidly as possible” its administration. 

“The United Nations said, ‘Shame on you, U.K., shame on you, bad, bad, bad, bad,’” Senator Kennedy said recently on the Senate floor. “You have to give back the Chagos Islands and the military base there.” And “not only do you have to give it back, but you don’t give it back to the people of the Chagos Islands, you give it back to another group of islands way down here, called Mauritius.”

Mr. Starmer, who took over at London’s 10 Downing Street last July after 14 years of Conservative-led governments, heeded the ICJ’s ruling, and negotiated a deal with Port Louis: Britain would transfer sovereignty to Mauritius, but would lease access to Diego Garcia for 99 years. 

Earlier this month Labour officials denied as “categorically untrue” press reports that following a renegotiation, the lease price would nearly double to 18 billion British pounds a year from nine billion, the equivalent of more than $11 billion.

“This is insane, this is down to the bone, deep down to the marrow stupid,” Mr. Kennedy said. “Because the United Nations wants the United Kingdom to feel guilty” about its colonial past, “they want to give our military base and their military base to Mauritius.”

Mr. Starmer can still stop the sovereignty transfer of Diego Garcia to Mauritius, Mr. Kennedy stressed. “Marco Rubio, our new Secretary of State, is against it. And I haven’t talked to him directly, but I think President Trump is against it,” he added. 

Opposition to the deal is also growing across the pond. “This is a very unpopular deal in Britain,” Mr. Gardiner, now with the Heritage Foundation, tells the Sun. “There’s a huge amount of parliamentary opposition to it,” so Mr. Trump “would do a huge favor to the U.K. if he blocks the deal. If he opposes it I don’t think that Starmer can realistically move forward with the deal.”

Ironically, then, Mr. Trump could even help Mr. Starmer to save face, rescuing him politically from a deal that is widely disliked at home, Mr. Gardiner adds.

Britain has administered the Chagos islands since the early 20th century. In 1942, at the height of World War II, it built an air field at the island of Diego Garcia. Since 1971, both American and British forces have been stationed at the atoll, symbolizing  the “special relations” between the countries.

Mr. Starmer’s arrival at the White House Thursday will be marked by likely friction between the premier, who is backed up by most of Europe, and the president. While most attention will be paid to Ukraine and the continent, the fate of Diego Garcia could end up most consequential for the relations across the pond.