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Days away from commemorating the 75th anniversary of the D-Day invasion — an enduring symbol of the U.S.-British alliance — President Donald Trump offered his own special rhetorical contribution to mark the occasion: He offered a succession of insults to the prime minister, a member of the royal family and the mayor of London.

Trump’s barbs ahead of his arrival in London on Monday affirmed the American leader’s seeming inability to rise above pettiness. During his previous visit last year, Trump was repeatedly goaded by British protesters who flew a big balloon depicting him as a baby in diapers. The balloon appropriately flies high again in the skies over central London.

“We know Trump isn’t a joke. … But if flying a balloon caricature is what gets under his skin — then that’s exactly what we’re going to do,” protest leader Anna Vickerstaff wrote in the U.K. daily The Independent.

It would be comforting for the world to rest assured that the person in control of America’s vast nuclear arsenal, who single-handedly could launch World War III, was someone capable of not letting such silliness get under his skin. Trump instead has proven time and again that he is willing to escalate any rhetorical battle to new heights of childishness.

Rather than respect Britain’s sovereignty and avoid meddling in its domestic affairs, Trump has plunged into it, offering a tacit endorsement of lawmaker Boris Johnson, the former London mayor, as a potential successor to Prime Minister Theresa May, who leaves office on Friday. He has repeatedly criticized May’s handling of talks over Britain’s withdrawal from the European Union.

Ahead of the 2016 presidential election, Johnson used phrases such as “stupefying ignorance” and “clearly out of his mind” in reference to Trump. The current London mayor, Sadiq Khan, has actually been more restrained, steering away from name-calling while questioning in a newspaper op-ed the red-carpet reception Trump was being given on this trip. In a tweet, Trump responded by calling Khan a “stone-cold loser” who has “done a terrible job” as mayor. A true leader would have ignored such taunts.

Ahead of the 2016 election, then-actress Meghan Markle indicated she would prefer not to live in the United States under a Trump presidency. She has since married Prince Harry and, as a member of the royal family, carries the title Duchess of Sussex. Ignoring protocol, Trump referred to her as “nasty” in a weekend interview with a British tabloid. Then he denied having used the word. The newspaper produced an audio recording to prove it.

Against that backdrop, it’s hardly surprising that Trump has not been invited to address Parliament, while some members of Parliament declined an invitation to a state dinner. Such honors are correctly reserved for statesmen — a word Trump might consider adding to his vocabulary sometime.