The reviews are in: The British press say King Charles III delivered a masterful diplomatic rebuke of President Trump this week, in an ever-so-polite royal way.

“King delivers hard truths” read a headline in the Daily Mail, praising him for urging the United States to defend NATO and Ukraine. A journalist at The Sun called him “Britain’s No.1 diplomat.” The Independent said Charles chided Mr. Trump with a “combination of eloquence and élan,” speaking in “such nuanced and sophisticated terms that even Trump and his volatile supporters could not take offense.” The New Statesman said it was “politics couched in regal tones.”

To many Americans, the sharp edges of the king’s seemingly tactful message may not have been apparent. And even Mr. Trump seems to have been oblivious to the fact that Charles was gently taking him to task. After waving goodbye to the royal couple Thursday morning, the president turned to reporters and said: “Great people. We need more people like that in our country.”

The king is, of course, British, and like his fellow countrymen, can be famously indirect. Americans looking for blunt or obvious statements were always going to be disappointed.

Britain’s constitutional monarchy requires, as Buckingham Palace puts it, that the king remain “politically neutral on all matters,” including, presumably, while interacting with the volatile leader of one of the country’s closest allies.

But citizens of the king’s commonwealth are by now used to reading between the lines, looking for symbolic gestures or stinging criticism couched in wry humor and ambiguous deflection.

Charles is, after all, the son of Queen Elizabeth II, who in 2017 famously wore a blue hat with yellow flowers — the colors of the European Union flag — to open Parliament a year after the Brexit vote, suggesting to many that she was showing her sympathies with the broader European cause. And last year, the king wore Canadian military honors on his uniform not long after Mr. Trump began threatening to make the country the 51st U.S. state.

Of course no one can really get inside the king’s head, and speaking obliquely can offer a level of plausible deniability. But anyone with even a glancing knowledge of the values and causes that Charles espoused when he was Prince of Wales — environmentalism, religious pluralism, tolerance and multiculturalism — could guess at his likely ideological differences with the president. The question before the trip was whether any hint of conflict would surface, or whether it would remain submerged in diplomatic niceties.

To many British observers, the king’s public speeches this week — deliberate messages, carefully composed with the help of diplomats and others in the government — were far stronger than expected, at several moments directly contradicting Mr. Trump’s policies and his administration’s approach to the world.

There were undeniable efforts during the king’s speech to Congress to push back against the president’s attacks on Prime Minister Keir Starmer (“As my prime minister said last month: ‘Ours is an indispensable partnership,’” said Charles), as well as comments championing NATO and the need for a “stable and accessible” rule of law.

There was the call for “unyielding resolve” in the defense of Ukraine. The moment that the king recounted his own, proud service in a Royal Navy as a rejoinder to the president calling British ships “toys.” And the part about a “shared responsibility to safeguard nature” to a president who has gutted environmental rules.

All of this was couched in dry wit and the king’s vintage upper-class English; he actually said “by Jove!” in his remarks at the Capitol and tried hard to make a Hollywood cultural reference by calling the founding fathers of the United States “rebels with a cause.”

There was the joke about how the British have everything in common with America “except, of course, language.” And the moment when the king joked about Mr. Trump’s new White House ballroom, recalling the “small attempt at real estate redevelopment of the White House in 1814,” a cheeky reference to when the British burned down the building.

“You recently commented, Mr. President, that if it were not for the United States, European countries would be speaking German,” the king quipped during his toast at the state dinner. “Dare I say, if it wasn’t for us, you’d be speaking French.”

The approach could have been high risk because Mr. Trump is so thin-skinned and almost never makes self-deprecating jokes. But the humor appears to have charmed, not infuriated, the president. On Thursday afternoon, he announced on his social media account that he was eliminating a tariff on Scotch whisky, saying that “the king and queen got me to do something that nobody else was able to do, without hardly even asking.”

There are few places where the king’s words are dissected more completely than in British newsrooms, where a designated group of reporters cover the royal family exclusively.

The Sun newspaper hired a lip reader to see what the two men might have said to each other. (The conclusion? Trump supposedly asked the king: “Are you drunk?”) Not to be outdone, The Mirror contacted a body language expert to decode the dynamic between the king and the president. (That person decided that Charles seemed nervous upon his arrival at the White House: “Whatever is going on in his mind, he is telling himself it’s OK, it will be fine, calm down,” they suggested.)

Online, a virtual army of amateur royal sleuths have been publishing video clips showing the interactions between the king and the president over the last several days.

One person posted a short clip to Instagram of the king’s face when the president joked about his mother’s conclusion that “little Charles” was “so cute.” Charles flashes a bit of an embarrassed smile and a royal wave of his right hand.

Several people who seemed not so fond of Mr. Trump posted video of the moment that the president walked in front of Queen Camilla and started shaking hands with people in the crowd gathered on the South Lawn of the White House.

As many noted, there were a couple of royal faux pas there: You’re not supposed to walk in front of the queen like that. And Mr. Trump effectively prevented the king from shaking hands with the crowd as well.

Zooming in on the video to look at the king and queen’s expressions reveals perfect poker faces — not betraying whatever they might be thinking. Which is something that Charles, in particular, has been trained to do all his life.

“The monarch in his role, he’s so careful about disclosing his own particular position,” said Arianne Chernock, a historian at Boston University. “The monarch, and his family by extension, they are always a screen onto which we project our beliefs.”