LONDON – The outlook for American-British relations looks bleak, at least to judge from the choice of Britain’s next ambassador to Washington. A figure in the Labour government of prime minister Tony Blair more than 20 years ago, Lord Peter Mandelson, has left no doubt what he thinks of President Trump. 

“Reckless and a danger to the world,” is how Mr. Mandelson described Trump to an Italian journalist during the president-elect’s first term. Mr. Mandelson will surely shy away from such language when he gets to Washington, but it’s not likely his harsh words in the past will be quickly forgotten. 

“An absolute moron,” one of Trump’s closest aides, Chris LaCivita, posted on X. He contrasts Mr. Mandelson to the outgoing British ambassador in Washington, Karen Pierce, whom he called a “professional universally respected ambo.” 

More specifically, Mr. Mandelson, as European commissioner for trade in 2018, warned in a British newspaper it was “necessary to recognize Mr. Trump’s behavior for what it is: he is a bully, and the U.S. will gain in trade only when others are losing.” 

Trump’s “idea of a progressive trade policy,” he wrote, “is one that forces everyone else to give the U.S. more favorable treatment rather than a trading system from which everyone gains.” Trump has often called for an aggressive policy on trade, including elevated tariffs, but Mr. Mandelson’s overall tone has upset Trump and his aides. 

“Trump aide’s Mandelson jibe was clearly designed to stir things up — but why?” asked the British television network Sky News. Mr. LaCivita’s remark was “awkward for Downing Street to say the least,” the network added. 

By appointing Mr. Mandelson to such a visible, critical post, however, the prime minister, Keir Starmer, may be sending a signal to Washington — that Britain intends to get tough with President Trump on issues ranging from trade and tariffs to the North Atlantic Treaty Organization and the war in Ukraine.

Between the lines of honeyed words in a statement from Mr. Starmer announcing the appointment, it seemed clear that Mr. Mandelson will do more in Washington than engage in diplomatic pleasantries. “Peter will bring unrivalled experience to the role and take our partnership from strength to strength,” Mr.  Starmer’s office quoted him as saying.

Mr. Mandelson was slightly more forthcoming, according to the announcement, when he acknowledged, “We face challenges in Britain, but also big opportunities and it will be a privilege to work with the government to land those opportunities.”

Exactly what he had in mind was left unclear, but there’s no doubt Britain and America aren’t getting along quite so famously as, say, President Reagan and Prime Minister Thatcher.