What happens when politicians are caught saying impolitic things?

This week, Prime Minister Justin Trudeau of Canada appeared to become the latest in a long line of world leaders who say how they really feel in private company, only to realize later that their remarks have been recorded and transmitted across the globe.

While at a NATO anniversary celebration in London, Mr. Trudeau spoke to a close circle of notable figures, including President Emmanuel Macron of France, Prime Minister Boris Johnson of Britain and Prime Minister Mark Rutte of the Netherlands .

In a video of the conversation that went viral, Mr. Trudeau can be overheard making a reference to President Trump’s affinity for news media attention.

“He was late because he takes a 40-minute news conference at the top,” Mr. Trudeau said of the American president.