President Trump arrived in Britain on Monday for a three-day state visit that will combine royal pomp and circumstance, and high-level talks with Prime Minister Theresa May.

Mr. Trump began the day in his typically unpredictable manner, taking shots at Mayor Sadiq Khan of London on Twitter, even before his plane had landed. But the scripted portion of the day was devoted to ceremonial activities devoid of politics with the royal family.

After a brief stop at the residence of the American ambassador, the president had lunch with Queen Elizabeth II at Buckingham Palace. That was to be followed by the laying of a wreath at Westminster Abbey, tea with Prince Charles and his wife, and a state banquet later in the evening.