US President Donald Trump left for a historic second state visit to Britain Tuesday -- but political controversies, wars and tariffs threatened to cloud the pomp and pageantry.
Britain is rolling out its royal family in a bid to woo the mercurial Trump, with security tight as protesters gear up to make their voices heard against the 79-year-old.
Trump, whose mother was Scottish and who has long been fascinated by the British monarchy, was full of praise for his "friend" King Charles III as he left Washington.
The Republican is the first US president to be invited for two state visits, after previously being hosted by Queen Elizabeth II during his last term in office in 2019.
"Charles, as you know, who's now king, is my friend," Trump told reporters at the White House before leaving hand-in-hand with First Lady Melania Trump. "He's such an elegant gentleman and he represents the country so well."
But Trump indicated that embattled Prime Minister Keir Starmer will still have his work cut out as Britain seeks to put the finishing touches on a deal to avoid the US president's sweeping global tariffs.
"They want to see if they can refine the trade deal a little bit," Trump said.
Controversies over sex offender Jeffrey Epstein and free-speech culture wars, and Starmer's political troubles at home could also make for some awkward moments.
- 'Huge moment' -
Trump was due to arrive Tuesday evening and then head to Windsor Castle outside London on Wednesday, for a full day of lavish events hosted by Charles.
He will be honoured there with a carriage procession and a grand state banquet.
The setting means he will be far away from crowds and protesters, with his schedule due to avoid London where a large anti-Trump demonstration has been called on Wednesday.
Security is being ramped up in Windsor too, with police saying they had deployed a marine unit and drones around the area.
After Windsor's pageantry, politics will dominate on Thursday when Starmer, who has worked hard to win over Trump since his return to power, hosts the US president at his country retreat Chequers.
The visit is "a huge moment for both" men, said Evie Aspinall, director of the British Foreign Policy Group think-tank.
"For Trump, the state visit is an opportunity to revel in the pomp and ceremony he loves," she told AFP.
"For Starmer, the visit is a chance to distract from domestic discontent and shift the limelight onto international issues where he has had greater success."
Starmer desperately needs the visit to go well following a miserable few days in which some of his own Labour party members have openly questioned whether he can remain as leader.
He has been dogged by questions over his judgement for appointing the now-sacked Peter Mandelson as ambassador to Washington despite his known friendship with the late Epstein.
Trump is facing awkward scrutiny himself over his own links to the convicted sex offender. Activists on Monday unveiled a huge portrait of Trump and Epstein on a large patch of grass outside Windsor Castle.
The White House meanwhile said Trump would bring up free speech with Starmer -- a topic raised by Trump's former ally Elon Musk in a televised speech to a far-right rally in Britain over the weekend.
- 'New heights' -
On foreign policy there are differences too.
Britain is one of a number of US allies moving to recognise a Palestinian state, as Israel launches a new offensive in Gaza, but Washington strongly opposes the idea.
On Ukraine, Trump said he would be pressing London and other European capitals to impose sanctions on China to get it to stop backing Russia.
But Downing Street has said Trump's visit would see the "unbreakable friendship" between the countries "reach new heights".
The two nations are set to sign a raft of agreements worth £10 billion ($13.6 billion) on nuclear and tech projects.
Google said it would invest £5 billion in the UK in the next two years while US finance firms including PayPal and Citi Group announced they would spend £1.25 billion.
Meanwhile, Melania Trump is also set to cause a stir with her separate itinerary on Thursday -- a rare public appearance for the Slovenian-born first lady.
She is due to take part in an event with Queen Camilla, who is recovering from a bout of acute sinusitis which prevented her from attending the Duchess of Kent's funeral on Tuesday.
A.Gerard--LCdB