After U.S. President Donald Trump doubled down on his belligerent and incoherent trade threats during the G7 summit in Quebec City on Saturday—at one point suggesting the U.S. would "stop trading" altogether with Canada, Europe, and Japan—Canadian Prime Minister Justin Trudeau announced that he would move forward with "retaliatory, equivalent tariffs," matching Trump's recently announced steel and aluminum penalties.

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JUST IN: Canadian Prime Minister Justin Trudeau says he will impose retaliatory measures to answer President Trump's tariffs on steel and aluminum: "Canadians: we're polite, we're reasonable, but we also will not be pushed around." https://t.co/kOFlnuMaEH pic.twitter.com/32vYsYdtwP — CNN (@CNN) June 9, 2018

Trump was quick to respond to Trudeau's announcement in a Twitter outburst Saturday evening, writing that he will instruct U.S. representatives at the G7 summit to not sign the joint communique the seven nations crafted after a series of compromises and threatening to impose tariffs on automobiles from Canada.

Based on Justin’s false statements at his news conference, and the fact that Canada is charging massive Tariffs to our U.S. farmers, workers and companies, I have instructed our U.S. Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market! — Donald J. Trump (@realDonaldTrump) June 9, 2018

"The U.S. is officially in a trade war with Canada," Buzzfeed reporter David Mack wrote in response to Trump's tweet.

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Trudeau's decision to move ahead with retaliatory tariffs capped off a tense day of discussions between the U.S. president and other world leaders, in which Trump—as many commentators were quick to point out—repeatedly demonstrated his ignorance of trade policy and made some of the most "nonsensical" claims of his presidency.

As Toronto Star reporter Daniel Dale observed, Trump spent much of the G7 summit "painting a highly inaccurate tariff picture—wrongly suggesting everyone else has high tariffs while U.S. has none."

Trump is painting a highly inaccurate tariff picture - wrongly suggesting everyone else has high tariffs while US has none. Here's a World Bank graph of trade-weighted average tariffs for the G7 countries - with US nearly identical to UK/Italy/France/Ger, higher than Japan/Can. pic.twitter.com/nuTkj7Xl6L — Daniel Dale (@ddale8) June 9, 2018

As Common Dreams reported after Trump decided to slap Canada, the European Union, and Mexico with steel and aluminum tariffs, trade experts and lawmakers have repeatedly denounced Trump's push for a trade war with America's major allies as a "reckless" maneuver that could end up costing the U.S. hundreds of thousands of jobs.

Responding to the latest back-and-forth between Trump and Trudeau on Saturday, Rep. Ted Lieu (D-Calif.) wrote: "Soon Donald Trump will see that, unlike Republican members of Congress, other countries don't just say how high when Trump says jump. Trade is complicated and there are good deals and bad deals. But the president starting a trade war is stupid and hurts Americans."