President Donald Trump reportedly justified the tariffs he placed on Canadian steel and aluminum by asking Canadian Prime Minister Justin Trudeau in a phone call: “Didn’t you guys burn down the White House?”

CNN reported on the exchange, citing sources familiar with the call. The British burned down the White House in the War of 1812, when Canada was a British colony. CNN reported the President may have been joking, but the tariffs, justified on national security grounds by the Trump administration, have left Canadians furious.

“To the degree one can ever take what is said as a joke,” one source “on the call” told CNN, when asked if Trump meant the comment as a joke. “The impact on Canada and ultimately on workers in the U.S. won’t be a laughing matter.”

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