The president and the first lady will be hosted by King Charles III and Queen Camilla at Windsor Castle. Mr. Trump will also travel to the prime minister’s country residence, Chequers.

Nostalgia for the fashion and culture of the years after the millennium, when the future held promise for many, is a commentary on today’s mood.

The president said the vessel was heading to the United States, but he did not offer details about its location. Legal specialists condemned the action as illegal.