“THERE’S A special place in hell” for leaders such as Canadian Prime Minister Justin Trudeau, White House trade adviser Peter Navarro said on “Fox News Sunday.”

This, as President Trump was about to sit down with the head of a totalitarian North Korean regime responsible for crimes against humanity without parallel in the contemporary world, as a U.N. commission reported four years ago.

What could account for such White House savagery against a historic U.S. ally? Mr. Trudeau had engaged in “bad-faith diplomacy,” Mr. Navarro maintained. “He really kind of stabbed us in the back,” Larry Kudlow, head of the National Economic Council, agreed on CNN’s “State of the Union” on Sunday.

How so? Mr. Trudeau said at a news conference at the end of a tense Group of Seven summit that U.S. tariffs on Canadian steel and aluminum were “kind of insulting,” because Mr. Trump cited national security to erect them. This is nothing all that different from what Mr. Trudeau had said before. It is also a mild reaction relative to the sheer irrationality of the president’s increasingly unmoored trade policy.

In fact, Canada has every right to be insulted that Mr. Trump would invoke national security in their trade dispute. Canada has stood with the United States in every modern war and crisis. There is no doubt the United States could rely on Canadian steel and aluminum if another crisis developed, obviating the stated rationale for imposing the tariffs. Same goes for auto imports from Canada, another good on which Mr. Trump is threatening tariffs. In fact, the Trump administration’s concerns about Canadian trade center on relatively insignificant concerns, such as the treatment of U.S. dairy products. The United States is not facing a dangerous dairy emergency, and it never will. Wildly exaggerated economic grievances, not national security, are driving Mr. Trump’s trade agenda.

Even on those terms, Mr. Trump’s trade offensive is an insult. The United States maintains a largely free and fair trading relationship with Canada. On Mr. Trump’s favorite measure, the trade balance, the United States maintains a small surplus with Canada, with each side selling about $335 billion worth of goods and services to the other in 2017. Though Canada’s protectionist dairy policies are indefensible, dairy represents only a sliver, at 0.2 percent of U.S. exports to Canada, which is why past presidents would never have considered blowing up the relationship over complaints about milk prices. People and businesses are stitched tightly to one another across the United States’ northern border, and a disruption in the relationship could be devastating for those who rely on the free crossing of goods and people.

Mr. Kudlow suggested that Mr. Trump might have been deploying extra bravado to demonstrate strength before his meeting with North Korean dictator Kim Jong Un. In fact, he was demonstrating moral and strategic obtuseness. To alienate allies while fawning over dictators is not a sign of strength.

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