WASHINGTON — By the time he left London on Wednesday, President Trump somehow ended his state visit there a full 360 degrees from where he started. Which was referring to the Duchess of Sussex, the American-born Meghan Markle, as “nasty.”

Assessing the perceived degree of nastiness of the duchess in an interview before he left the United States kick-started an Orwellian saga — one that the president single-handedly created, forcefully denied and then revived again just before jetting off for the next leg of his European tour.

The fracas began with an interview with the British tabloid The Sun last weekend, when Mr. Trump was recorded saying that he was not aware that the duchess had made “nasty” comments about him during the 2016 presidential campaign.

“What can I say?” Mr. Trump said. “I didn’t know that she was nasty.”

It was not the way previous American presidents have let the British know they were coming. The reaction to a sitting president commenting on the perceived nastiness of a member of Queen Elizabeth’s family — who put on a state dinner at Buckingham Palace, to impress and placate him — was reliably parsed along tribal lines.