Boris Johnson Cuts a Colorful Swath in U.S., but to What End?

U.K.’s prime minister makes headlines, yet experts say it is unclear if his lighthearted style is helping stake out a post-Brexit role on the global stage.

LONDON — He told the world to grow up and accept the challenge of climate change. He made fun of France’s neuralgic reaction to being elbowed out of a submarine deal with Australia by Britain and the United States. He even cleared up lingering confusion about how many children he has (six).

Prime Minister Boris Johnson of Britain cut a characteristically colorful swath from New York City to Washington this week, managing to travel between the cities by Amtrak — a nod to his Amtrak-loyal host, President Biden — before telling the aggrieved French to “prenez un grip” and “donnez-moi un break.”

For Americans, now used to a president who rarely strays from the script, it was a throwback to a time when their own leader would show up in Britain and start lobbing cherry bombs. Except in the case of Donald J. Trump, that involved calling London’s mayor a “stone-cold loser” and telling a British tabloid that Mr. Johnson’s predecessor, Theresa May, was doing a bad job of negotiating a Brexit deal.