King Charles must be pinching himself at the moment. After months and months of terrible headlines, he's suddenly surrounded by applause.

Over the past couple of days, in his speeches on his US state visit, he's teased President Trump, stood up to him, charmed him and even though it was hidden in a velvet glove, landed a couple of decent digs.

And many commentators, even critics of the monarchy, seem delighted at the spectacle. It was the underdog winning the cup against all expectations.

Alastair Campbell, a longstanding republican, posted: "Excellent speech by King Charles... Loved the confidence in British and European values."

Sir Anthony Seldon, historian and biographer of prime ministers, praised the subtlety of what the King seemed to have pulled off.

"With a president known for his unpredictability and fresh out of an assassination attempt, the King managed to land subtle blow after blow on a smiling president, upholding Ukraine, Nato, climate change, the Royal Navy, and the limits to presidential authority," said Sir Anthony.

He described it as "a state visit for the ages, the most significant since his grandfather George VI's visit in 1939 on the eve of the Second World War".

Emily Maitlis, interviewer of Prince Andrew in the Newsnight interview, made bigger claims, hailing the speech for cheering up the nation.

"You send somebody out there and everyone applauds him and he carries it off. He did a sort of Love Actually speech, but written by Plato. That's what it felt like, someone who lifted us all up a bit," she said, in her Newsagents podcast.

For those inside the Capitol chamber, and I had the good fortune to be there watching, it was remarkable how quickly the mood became so noisily supportive. And it was certainly not what was expected.

Let's be honest, the multiple scandals about Andrew Mountbatten-Windsor have really put the royals on the ropes.

King Charles sometimes has the melancholy look of someone who keeps getting disappointing phone calls.

And again, to be frank, the mission to the US to rebuild bridges did look fraught with danger.

The political spat between President Trump and Prime Minister Sir Keir Starmer was showing no signs of settling.

The days running up to the state visit had been dogged by questions about meeting Epstein survivors. And when the King was about to travel, the shooting incident in Washington brought fresh calls for him to call off the trip.

A public opinion poll from Ipsos a few days before the trip suggested only a third of people expected the state visit to have a positive impact - and less than a quarter believed that a special relationship between the US and UK actually exists.

So when the King first cleared his throat, and looked down at the wide-spaced printed pages of his speech, looked around the crowded chamber, it was far from obvious that this was going to be such a barnstorming success.

It was only meant to be 20 minutes long but in the end he got 12 standing ovations. No one saw that coming.

It seemed to appeal across the political divide. Senator Lindsey Graham, a staunch conservative Republican, said: "Simply put: The King nailed it."

"The speech was a terrific combo of wit, humor, history and appreciation. I believe most members of Congress feel better after the speech than they did before."

Another Republican, Nikki Haley, former US ambassador to the UN, posted: "Amazing to see King Charles unify Congress in a way America craves."

The New York Times said the King "worked the House chamber like a stand-up comedian".

The scourge of the royals recently has been Andrew Lownie, author of the book that revealed so much Andrew Mountbatten-Windsor, and he was taken aback by a "brilliant speech".

"There are fair criticisms to be made of Charles, especially when it comes to how the Crown has dealt with Andrew Mountbatten-Windsor, and it's important that these continue to be made until the necessary reforms are enacted," says Lownie.

"However the King's visit is a perfect example of why I am a monarchist despite what my critics might suggest," he said.

"The worry had been that Trump would humiliate or embarrass the King, but history will likely record that it was the other way around," said the best-selling historian.

A former diplomat, Lord Peter Ricketts, told US National Public Radio: "This was frankly, the most difficult, demanding piece of royal diplomacy he's done so far."

"But he's got a tremendous sense of humour, as Americans will have seen over the last day."

Perhaps what made it work for people in the UK was the sense of someone standing up for them, after hearing President Trump's multiple criticisms for so long.

And doing it with humour hit all the sweet spots. It made it feel less like a fight.

With three of the four days of the visit now over, the speeches will be what's remembered here, as the security is so tight there have been no moments so far to meet the public.

Of course, this sudden international popularity for the King could be as fickle as a holiday romance.

Once he's away from the bright lights of the US, he'll be back home to the questions about Andrew, MPs will be digging round his finances and there will inevitably more front pages about Prince Harry.

But it's quite possible, that at some point in the future, when there are clips being played of King Charles's most successful moments of his reign, we'll be watching that speech in the US Congress, and those US lawmakers so unexpectedly cheering him to the rafters.

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