King Charles and Queen Camilla arrived at Joint Base Andrews in Maryland on Monday for a state visit in Washington, a city still rattled by a weekend shooting and a transatlantic alliance showing fresh signs of strain.

British flags could be seen lining lamp-posts outside the White House, where Donald Trump and the first lady, Melania Trump, were set to host the royals for a private tea and a tour of the newly expanded White House beehive on the south lawn.

“First Lady Melania Trump has led all of the preparations for the state visit which will honour the longstanding and special relationship between the United States and the United Kingdom,” Karoline Leavitt, the White House press secretary, told reporters on Monday.

But the four-day tour, intended to mark the 250th anniversary of US independence, begins against the backdrop of a diplomatic rift over Trump’s war in Iran and a dramatic security scare at last Saturday’s White House Correspondents’ Association dinner.

A gunman opened fire inside the Washington Hilton hotel, prompting Secret Service agents to rush the president from the dais. Officials believe the president and members of his administration were the likely targets and the incident prompted an urgent review of security arrangements before the king’s arrival.

For Charles, the posture will be “keep calm and carry on”. Buckingham Palace said the visit would proceed after consultations with US authorities. A spokesman said: “The King and Queen are most grateful to all those who have worked at pace to ensure this remains the case.”

The king will speak at a packed state dinner in the White House East Room and in a rare address to the US Congress, where some commentators expect him to dwell on the importance of culture and civilisations – an exquisitely subtle reminder that adversaries such as Iran have enduring civilisations of their own.

Charles will then travel to New York to visit the September 11 memorial, alongside the New York mayor and rising political star Zohran Mamdani, before concluding in Virginia, where he will meet conservation groups, reflecting a cause he has championed for more than half a century.

Some British politicians worry that the king’s soft power mission is fraught with opportunities for embarrassment, with Trump’s recent attacks on Pope Leo XIV intensifying the concerns.

Relations between the two allies have been bruised by Trump’s public criticism of Britain’s refusal to back military action against Iran. In recent weeks the president has derided the prime minister, Keir Starmer, as “no Winston Churchill”, while leaked Pentagon discussions about revisiting US support for British sovereignty over the Falkland Islands have deepened unease.

Yet Trump, who places an unusual emphasis on the diplomatic role of monarchs in Saudi Arabia and other countries in the Middle East, has carefully separated his admiration for the king from his frustrations with the government. He has repeatedly described Charles as “a great man” and “a friend”, and suggested the royal couple’s presence could help steady relations between the two countries.

Christian Turner, the British ambassador to the US, told CBS’s Face the Nation programme on Sunday: “We had a small difference of opinion in 1776. We’ve been through that. We’ve come a very long way and that, in a way, for me, is what is so enduring about these relationships. It’s that we’ve had differences. Thatcher to Reagan, Roosevelt with Churchill, actually, over how to handle Stalin. These are moments in the relationship that actually it endured because it is so deep on security.”

However, the continuing scandal surrounding the king’s younger brother, Andrew Mountbatten-Windsor, and his links to the convicted sex offender Jeffrey Epstein, have again surfaced ahead of the tour.

Ro Khanna, a Democratic congressman, is convening Epstein survivors on Capitol Hill on Tuesday and urging the king to meet them. He said: “The British people have actually been very strong on this Epstein matter, demanding accountability and justice – stronger than the American government in terms of taking action. So the king doesn’t have to get into any details of his brother’s case but it’s just standing with survivors and calling for accountability around the world.”

The British journalist Emily Maitlis said on the News Agents podcast she had been told that, until two weeks ago, Queen Camilla was “very keen” to meet victims of Epstein alongside Melania Trump. Maitlis added: “She said, ‘I’ve spent my life fighting for women’s voices, I’ve spent my life fighting for victims, we will find a way to do it.’”

But palace officials have made clear there will be no meetings with Epstein survivors during the trip, citing legal concerns over ongoing investigations in the US and Britain.

Charles has visited the US 19 times but this is his first state visit to the country since becoming king in 2022. His mother made four state visits to the country.