British ambassador to USA forced out for telling it like it is

Much as I hate to mention the name again, Donald Trump has forced the British ambassador to the USA to resign after having a hissy fit in response to leaked emails from the ambassador.
Respected British career diplomat Sir Kim Darroch resigned after Trump petulantly tweeted that he and his administration "will no longer deal with him", putting Darroch in an untenable position. And Darroch's crime? Daring to criticize the Trump administration in private internal emails, including comments like, "We don't really believe this administration is going to become substantially more normal, less dysfunctional, less unpredictable, less faction-riven, less diplomatically clumsy and inept", and bemoaning the "infighting and chaos" within the White House.
So, really, just what everyone else had been saying for years now. Is Trump really unaware that the rest of the world, and at least half of America, hates him, and has zero confidence in his administrative and leadership abilities? Does he not realize that people talk about him like this (and much worse) all the time? Is no criticism now permissible? And is he really that thin-skinned after his years in power? Trump's response - not private, but tweeted for all the world to see - was much more offensive, as he called Darroch "wacky", " a very stupid guy" and "a pompous fool", as well as laying into Theresa May and Britain in general. But this is apparently not grounds for  resignation in his case.
And then, of course, there's the whole issue of how all this came to light. An internal inquiry has been called into the leak, and the possibility of a criminal investigation has been raised. Why would anyone have leaked such private emails, knowing full well that an international incident was almost certain to be provoked? Money, I can only conclude. And, of course, it was the Mail on Sunday that published it (paid for it?), not a reputable paper, and they have a good deal of responsibility for the whole fracas.
But the biggest culprit? I have to say Donald J. Trump, for his wild and excessive reaction, his narcissism and his bullying tactics.