AMNA NAWAZ: Welcome to the "News Hour."

Canada imposed retaliatory tariffs against the United States today, as the two neighbors slide toward an all-out trade war.

GEOFF BENNETT: The tariffs will hit a range of U.S.

products, from industrial goods to everyday items.

At the same time, President Trump is threatening Canada with even steeper tariffs.

William Brangham begins our coverage.

WILLIAM BRANGHAM: In Ottawa today, Canada's government had a clear message: It's firing back.

FRANCOIS-PHILIPPE CHAMPAGNE, Canadian Finance Minister: Canada will meet the moment.

Canadians will meet the moment.

We will meet the moment together.

We will support our workers, our businesses and our industry with whatever it takes for as long as it takes.

WILLIAM BRANGHAM: Starting September 8, Canada will impose or raise tariffs ranging between 15 and 50 percent, affecting $27 billion worth of imports, and that will hit over 700 U.S.

products, including some key U.S.

imports.

FRANCOIS-PHILIPPE CHAMPAGNE (through translator): Our response will specifically target products in the sectors of steel, aluminum, household appliances, farming equipment, paper products, and electronics.

WILLIAM BRANGHAM: Canada's retaliation follows the Trump administration placing 50 percent tariffs on roughly $20 billion worth of Canadian imports on Saturday, along with threats of more to come.

President Trump said he will impose 50 percent on steel and autos starting next year.

And this clash between allies has gone beyond goods.

President Trump wrote on social media that the U.S.

doesn't expect to do business with the Canadian border province of Ontario, adding -- quote -- "The United States is giving serious consideration to changing the name of Lake Ontario to Lake America."

To that, one Canadian official simply said today: MELANIE JOLY, Canadian Industry Minister: We will always call it Lake Ontario, period.

(APPLAUSE) WILLIAM BRANGHAM: But for all the rhetoric, Trump last night did acknowledge the U.S.

relies on Canada for some key products like aluminum.

DONALD TRUMP, President of the United States: You know, selfishly, we need aluminum in this country.

We don't have it.

We get it all from Canada for the most part, and we need it badly.

WILLIAM BRANGHAM: President Trump has long lamented the trade deficit between the two countries, which stood at nearly $50 billion last year.

But for a trading relationship as big as the U.S.

and Canada's, these tariffs still hit just a fraction of the roughly $800 billion of commerce between the two neighbors, which U.S.

Trade Representative Jamieson Greer has echoed.

JAMIESON GREER, U.S.

Trade Representative: At the end of the day, this is 5 percent of imports from Canada.

It's 0.06 percent of our overall consumption in this economy.

So there's no possible way it can really affect U.S.

well-being.

WILLIAM BRANGHAM: Still, for states like Michigan, which trades heavily with the nation to its north, this trade war is already having consequences.

Michael Howard says his furniture business has started losing clients.

MICHAEL HOWARD II, Howard Family Designs: With a 50 percent tariff, all those costs have skyrocketed, and our -- just that one project has cost our family thousands of dollars in profit, and which impacts the ability for us to put food on the table for our family.

WILLIAM BRANGHAM: On the U.S.-Canadian border, where $2.5 billion in goods cross every day, the costs to citizens on both sides continue to grow.

For the "PBS News Hour," I'm William Brangham.