President Trump is on the cusp of upending North American trade, threatening to strike a radical blow to relationships with America's top economic partners.

Trump is expected to announce Saturday steep new tariffs on goods from Canada and Mexico, after pledging for months to impose import taxes on two close U.S. allies.

The president has left several questions about his plans unanswered, such as how high the tariffs might be, when they would be implemented, under which law they would be issued and which goods might be exempted.

Trump’s most aggressive proposal, however, would hit all Canadian and Mexican products with 25 percent import taxes. Experts say doing so would spur near-immediate increases in food and fuel prices, while prompting damaging retaliation from two countries deeply integrated into the U.S. economy.

“That would be a massive deal. These are America's two largest trading partners. We depend on imports from both of those countries, and your first-order impact is higher prices for American consumers and for companies,” said Edward Fishman, a senior research scholar and adjunct professor at Columbia University.

“And I think that's why you see a lot of people, including folks who supported President Trump, voice a lot of concerns,” added Fishman, author of the forthcoming book “Chokepoints: American Power in the Age of Economic Warfare.”

Trump himself has brushed off........

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