Later, Trump hailed his host -- Queen Elizabeth II -- as a "great, great woman" during a toast at Buckingham Palace, while the long-serving monarch offered a subtle endorsement of the international institutions Trump has at times criticized.

It was a stately day that came amid less dignified bickering between Trump and London's mayor, the elaborate displays of hospitality doing little to prevent Trump from dispatching insults over Twitter as he descended into London.

The President salutes troops as he and the first lady arrive at Stansted Airport.

The President salutes troops as he and the first lady arrive at Stansted Airport.

The Trumps walk toward Marine One after arriving at London's Stansted Airport on June 3.

The Trumps walk toward Marine One after arriving at London's Stansted Airport on June 3.

The Trumps arrive at Winfield House, the residence of the US ambassador, on June 3.

The Trumps arrive at Winfield House, the residence of the US ambassador, on June 3.

People outside Buckingham Palace photograph the Changing of the Guard ahead of Trump's arrival on June 3.

People outside Buckingham Palace photograph the Changing of the Guard ahead of Trump's arrival on June 3.

Trump's daughter Ivanka, who is also advisor to the President, looks out of a window at Buckingham Palace.

Trump's daughter Ivanka, who is also advisor to the President, looks out of a window at Buckingham Palace.

The US National Anthem is played during a welcoming ceremony at Buckingham Palace. From left are Melania Trump, the Queen, Trump, Charles and Camilla.

The US National Anthem is played during a welcoming ceremony at Buckingham Palace. From left are Melania Trump, the Queen, Trump, Charles and Camilla.

Among the items on display was "American Pewter Thoroughbred," a gift that Trump gave the Queen last year.

Among the items on display was "American Pewter Thoroughbred," a gift that Trump gave the Queen last year.

Queen Elizabeth II welcomes the Trumps to Buckingham Palace. She took them on a tour of the royal collection.

Queen Elizabeth II welcomes the Trumps to Buckingham Palace. She took them on a tour of the royal collection.

The Trumps are joined by Prince Andrew as they pay their respects at the Tomb of the Unknown Warrior in Westminster Abbey.

The Trumps are joined by Prince Andrew as they pay their respects at the Tomb of the Unknown Warrior in Westminster Abbey.

The President signed the guestbook at Westminster Abbey. "Thank you so much," his message said. "This has been a great honor. Special place."

The President signed the guestbook at Westminster Abbey. "Thank you so much," his message said. "This has been a great honor. Special place."

Trump stands next to Queen Elizabeth II before a state banquet at Buckingham Palace on Monday, June 3. Joining them are Melania Trump, Prince Charles and Camilla.

Trump and May are followed by their spouses as they make their way to the news conference in London on June 4. The President offered plenty of praise for May, who recently announced her resignation.

Trump and May give a joint news conference on June 4. "I think she's done a very good job," Trump said, reversing past critiques of her failure to strike a Brexit deal that both Parliament and the EU can accept.

Trump and May give a joint news conference on June 4. "I think she's done a very good job," Trump said, reversing past critiques of her failure to strike a Brexit deal that both Parliament and the EU can accept.

Brexit Party leader Nigel Farage, center, arrives at Winfield House, where the Trumps are staying during their visit.

Brexit Party leader Nigel Farage, center, arrives at Winfield House, where the Trumps are staying during their visit.

Melania Trump spends time with Camilla and Suzanne Ircha, the wife of the US ambassador.

Melania Trump spends time with Camilla and Suzanne Ircha, the wife of the US ambassador.

The Trumps pose for a photo ahead of a dinner at Winfield House in London on Tuesday, June 4. Joining them, from left, are Woody Johnson, the US ambassador to the United Kingdom; Camilla, the Duchess of Cornwall; Prince Charles; and Johnson's wife, Suzanne Ircha.

The Trumps pose for a photo ahead of a dinner at Winfield House in London on Tuesday, June 4. Joining them, from left, are Woody Johnson, the US ambassador to the United Kingdom; Camilla, the Duchess of Cornwall; Prince Charles; and Johnson's wife, Suzanne Ircha.

Trump meets with German Chancellor Angela Merkel on the sidelines of the D-Day event in Portsmouth.

Trump meets with German Chancellor Angela Merkel on the sidelines of the D-Day event in Portsmouth.

Britain's Queen Elizabeth II and Prince Charles play host to the Trumps at the D-Day event in Portsmouth. British Prime Minister Theresa May is at left.

Britain's Queen Elizabeth II and Prince Charles play host to the Trumps at the D-Day event in Portsmouth. British Prime Minister Theresa May is at left.

At a D-Day event held Wednesday, June 5, in Portsmouth, England, Trump reads a prayer that President Franklin D. Roosevelt gave over the radio on D-Day.

At a D-Day event held Wednesday, June 5, in Portsmouth, England, Trump reads a prayer that President Franklin D. Roosevelt gave over the radio on D-Day.

The Trumps are joined by French President Emmanuel Macron and his wife, Brigitte, as they watch a flyover on June 6.

The Trumps are joined by French President Emmanuel Macron and his wife, Brigitte, as they watch a flyover on June 6.

Trump and his wife, Melania, visit the graves of troops who died on D-Day.

Trump and his wife, Melania, visit the graves of troops who died on D-Day.

US President Donald Trump, visiting the Normandy American Cemetery in France, participates in a ceremony to commemorate the 75th anniversary of D-Day on Thursday, June 6.

US President Donald Trump, visiting the Normandy American Cemetery in France, participates in a ceremony to commemorate the 75th anniversary of D-Day on Thursday, June 6.

All-in-all, it was a fitting start to a visit laced with controversy and steeped in tradition, delivered by a fractured nation for a hard-to-please guest.

"I think it'll be very important," Trump predicted as he departed the White House on Sunday evening. "It certainly will be very interesting."

Indeed, the dramatics began even before Air Force One had touched down at Stansted Airport outside London. As he was descending, the President tweeted an insult of London's mayor, calling Sadiq Khan a "stone cold loser" for being "foolishly 'nasty' to the visiting President of the United States."

Trump and Khan have engaged in a transatlantic spat over terrorism and security, and this week Khan called Trump "one of the most egregious examples of a growing global threat" in a newspaper op-ed . Khan had suggested Trump's state visit should be rescinded.

His suggestion went unheeded, and on Monday Trump arrived in the UK for a day of royal pageantry.

The regal display of British soft power, with Trump and Queen Elizabeth II at the center , comes as the country find itself questioning its very identity amid a debate over exiting the European Union. Trump, who has not held back in offering his own options on Brexit, arrives at a deeply difficult moment as the prime minister prepares to step aside.

If those bitter undercurrents can't completely disappear, however, they were at least a sideshow as Trump and his extended family arrive in London to the type of stately welcome perfected by British royals over centuries.

His first call was at Buckingham Palace, where the Queen welcomed the President in the gardens as a guard of honor marched past and gun salutes were fired in nearby Green Park and from the Tower.

Wearing a mint-green hat and jacket, the Queen smiled broadly as Trump greeted her on the palace's West Terrace after alighting from his Marine One helicopter. The future king, Prince Charles, was the first to welcome Trump as he stepped out.

Later, the two men inspected a cordon of bearskin-hatted guardsmen, making small talk with the straight-faced men as they stood in the mild London sun.

Absent was a carriage ride down The Mall; protesters were expected to line the thoroughfare as Trump remains behind the palace gates.

He sat for lunch with the 93-year-old monarch, whom he met for tea last summer (and awkwardly walked in front of during a troop-inspecting ceremony in the courtyard of Windsor Castle).

She then took him on a tour of the royal collection, where artifacts of significance to America -- including an 18th-century map of New York, old time photos of a golfer at St. Andrews and a pewter horse statuette -- were on display. A keenly interested President spent ample time learning about the pieces from the Queen.

Prince Harry followed behind with Ivanka Trump and Jared Kushner, the President's children and senior advisers.

Later it was onward to Westminster Abbey for a wreath-laying ceremony and tour, and then to Clarence House for afternoon tea with Prince Charles, who has ardently warned of climate change for years. Trump told an interviewer this week he'd welcome a conversation with the Prince of Wales about the environment, though his administration is rolling back policies meant to curb carbon emissions.

In the evening was the centerpiece of the visit -- a state banquet back at Buckingham Palace, where both the Queen and Trump delivered toasts before a few hundred guests.

"As we honor our shared victory and heritage, we affirm the common values that will unite us long into future: freedom, sovereignty, self-determination, the rule of law and reverence for the rights given to us by almighty God," said Trump, dressed in white tie and tails for the highly formal occasion.

"From the Second World War to today, her majesty has stood as a constant symbol of these priceless traditions," Trump said at the start of the state banquet. "She has embodied the spirit of dignity, duty and patriotism that beats proudly in every British heart."

The Queen, meanwhile, appeared to deliver a subtle nod to the international bodies that were born from World War II.

"After the shared sacrifices of the Second World War, Britain and the United States worked with other allies to build an assembly of international institutions, to ensure that the horrors of conflict would never be repeated," she said. "While the world has changed, we are forever mindful of the original purpose of these structures: nations working together to safeguard a hard won peace."

The remark was understated, but notable coming as Britain continues to wrestle with its exit from the European Union -- a body with roots in the post-war period, when integration between countries was seen as a solution to violent nationalism.

Much of Britain's royal family participated in the visit, including Prince William and his wife Catherine, the Duchess of Cambridge.

Meghan Markle , the Duchess of Sussex, will not. She is on maternity leave after giving birth to her and Harry's first child last month. That is perhaps for the best; she had previously stated she would move to Canada if Trump was elected (she is American). Upon learning of those comments this week, Trump said he "didn't know that she was nasty," though went on to predict she would make a "very good" princess.

The invitation for a state visit was first offered more than two years ago, back when Prime Minister Theresa May's ill-fated destiny wasn't entirely clear and when Trump's pattern of insults and slights toward the United Kingdom had yet to develop.

In that span, the visit had been scheduled only to be canceled, with a stop in the UK last year downgraded to mere "working" status and organized to occur almost entirely outside London, where protesters flew a giant balloon depicting the President as a baby in a diaper.

The protesters, and the balloon, are back this week, and Trump will have a hard time avoiding them as he darts between royal engagements and meetings with May, one of her final acts before she steps aside as leader of her party next week.

Those talks will occur on Tuesday, and will include discussion of the Chinese tech giant Huawei, which the US is working to prevent from developing 5G networks in Europe and elsewhere. Trump will also host a breakfast of business leaders and another dinner, this one at the US ambassador's residence in Regent's Park.

Trump, who was largely gracious of May when she announced her decision, has since gone on to unfavorably characterize her handling of the Brexit muddle. He's showered praise on some of her political rivals: Boris Johnson, who once served in May's cabinet only to resign in protest, and Nigel Farage, a leader of the Brexit movement.

The White House has declined to say whether Trump will meet either Johnson or Farage while he's in London, though Trump told reporters before he left he'd like to see them.

But as of midday Monday, there aren't firm plans in place for such an encounter with Johnson, according to a US official. The official said that could change if Trump asks aides to arrange a meeting over the coming days.

The British government said it had no information about a potential meeting, indicating what Trump did in his private time was up to him.

If the timing for Trump's visit seems inopportune, officials point to the fact he's in Europe marking the 75th anniversary of the Normandy landings alongside leaders of other nations who fought in the war.

"You can't really put off D-Day," one official said.