The world's diplomats followed with considerable interest and trepidation as leaked cables from the UK's ambassador to the US, were published by a British Sunday newspaper, triggering a huge and ugly four-day row between Washington and London.
Unsurprisingly, the rowing culminated in the resignation of Sir Kim Darroch on Wednesday after President Trump had lit into him, for two days running, insulting him variously as "not well liked", "not serving his country well", "wacky", "very stupid" and "a pompous fool".
World capitals took note as he demeaned Mr Darroch, a knighted career diplomat with 42 years of public service under his belt, and an adviser to ministers and prime ministers, as foisted on Washington.
President Trump was staking a claim to a say in who serves as ambassador to Washington. And his unsolicited recommendation of 2017 that Mr Nigel Farage, his anti-EU friend, would make a good ambassador for the UK, assumed new significance.
As if addressing the next occupant of 10 Downing Street, Mr Trump accused Prime Minister Theresa May of "making a mess of Brexit" (Britain exits the European Union) by ignoring his advice and "going her foolish way" and courting "disaster". He declared her departure later this month "good news".
The President appeared intent on driving a dagger through the heart of the British government and diplomacy as well as jeopardising the special relationship between Washington and London, mooted and venerated, since the end of World War II.
Then came the last nail: President Trump disinvited Mr Darroch to a White House dinner on Tuesday. By implementing his Monday edict that Washington would "no longer deal" with Mr Darroch, he signalled government departments to sever links with the ambassador.
In one fell swoop, Mr Trump reduced a hero of UK's foreign service into a diplomatic zero and exposed Britain as weakened and isolated as it headed for the EU exits. Washington, to which London is looking for trade deals and stronger ties to fill the coming void, was deliberately helping diminish its international status.
Now a nobody in the world's political capital, and even though he was retiring in December, but firmly in the eye of the trans-Atlantic storm, Sir Kim put country first and paved way for a new ambassador. Bizarrely, he became the latest victim of the gluttonous three-year-old Brexit monster.
While Mrs May and Cabinet firmly backed Mr Darroch, Mr Boris Johnson, the man tipped to succeed Mrs May, and a self-professed friend of President Trump, refused to stand by the ambassador.
The President will be proud of Mr Johnson for helping him diminish London. And he will be proud of himself for taking on a diplomat of an ally and running him out of town as the world witnessed his muscle-flexing.
But why such animus against Sir Kim? These published choice quotes, among others, from his diplomatic dispatches dating back to 2017 when Mr Trump took the reins of power, hurt a President famous for a planet-sized ego and a notoriously thin skin:
"As seen from here we really don't believe that this administration is going to become substantially more normal; less dysfunctional, less unpredictable, less faction-riven. Less diplomatically clumsy and inept."
Then: "For a man who has risen to the highest office on the planet President Trump radiates insecurity."
And: "This America first administration could do some profoundly damaging things to the world trading system such as denounce WTO, could tear up existing trade details launch protectionist action, even against allies."
Diplomats in media interviews were unanimous on three things. One, Mr Darroch did nothing wrong. The job requires the holder to furnish his country with honest and unvarnished information about his hosts.
Two, the content of his cables, though stinging, was fair enough. But the last place a diplomat expects to see his dispatches is the media. What they write will anger many because of the sensitive issues and people they deal with. It is why the cables are kept secret and of limited circulation.
Three, the leak was treacherous, massively stabbed Sir Kim in the back and dealt British diplomacy a hammer blow. While many agree Trump was going to be angry, they did not think he would go for the diplomat and PM with all barrels blazing.
I draw three lessons for diplomacy from the row: Don't publicly get under President Trump's thin skin; he meddles at home and overseas; and a huge personal and national repair job awaits PM Johnson.