A diplomat for 29 years, Mr. Darroch has handled many of the country’s most sensitive international issues. He has served as Britain’s permanent representative to the European Union, as head of the Foreign Office’s press office and as national security adviser.
On Sunday, he declined to comment on the leak of the cables.
There is some history to the relationship between Mr. Trump and the British ambassador. Shortly after he took up the post in 2016, a memorandum by Mr. Darroch was leaked, suggesting that Mr. Trump would be “open to outside influence if pitched right.”
Mr. Trump then recommended, via Twitter, that his friend Mr. Farage, then the leader of the U.K. Independence Party, be appointed as ambassador to Washington in Mr. Darroch’s place. “He would do a great job!” Mr. Trump wrote.
A Downing Street spokesman responded swiftly then that Mr. Darroch had the government’s support.
While all the observations in the leaked cables have been echoed in books and news articles, it closely reflected the frustrations that Mr. Darroch and other foreign diplomats had reported during the period, as they sought to get access to the administration and feared that many long-running initiatives might run off the rails. Few of them had even conversed with the secretary of state at the time, Rex Tillerson.
But the trove included some more recent cables, including one written just hours after Mr. Trump reversed himself and decided not to go ahead with a military strike on Iranian bases after the shoot-down of an American drone.
Again, the cable described a chaotic policy process at the White House, though Mr. Darroch concluded that the president came out in the right place and avoided a bigger conflict — even if he got to the decision in the most meandering of policy debates, including consultations outside his own national security staff.
Among other revelations in the leaked cables:
• In a confidential letter dated June 27, 2017, and addressed to Mr. Sedwill and a handful of senior Downing Street figures, Mr. Darroch says allegations that the Trump camp colluded with Russia during the 2016 presidential campaign “cannot be ruled out.”