Canada on Tuesday announced tariffs on roughly $20 billion of U.S. goods, days after the U.S. escalated trade tension by enacting new levies on $20 billion of Canadian goods. The acrimony follows the collapse of trade talks between the two nations, which have a nearly $900 billion-a-year trading relationship. Canada's new tariffs are set to take effect Sept. 8.

Trade experts and economists said Canada's levies would exert pressure on Republican candidates running in key races in the U.S. midterm elections. Here's what they say about how the tariffs could affect the U.S. economy more broadly:

What is Canada tariffing?

Canada said it plans to impose tariffs of 15% to 50% on about $20 billion of U.S. imports. That equals roughly 7% of Canada's imports from the U.S. The levies are a "dollar for dollar" response to the U.S. decision to impose 50% tariffs on $20 billion of Canadian goods, effective Aug. 22, Canada said.

Canada said levies of 50% will affect steel and aluminum products that were previously subject to a 25% tariff, along with furniture and clothing. Goods facing 25% tariffs include appliances, dairy products and seafood.

Which industries and states are going to be hardest hit?

Canada's Industry Minister, Mélanie Joly, said the tariffs aim to exert political pressure in key races in the U.S. midterm elections in November.

Ed Gresser, a former assistant U.S. trade representative now working at the Progressive Policy Institute, said that was clear from the items Canada chose, including lobster and seafood. Half of the lobster caught in Maine goes to Canada, he said, and Maine has an important election this fall that will help determine control of the Senate.

"The states that are most reliant on Canada as an export market are often the northern-tier states-Maine, Michigan, Minnesota, Wisconsin, New Hampshire," Gresser said. Canada is "trying to show the Republican party that there's a systemic cost to doing this sort of thing."

Cheese and other dairy items Canada is targeting are produced in Wisconsin, New England and other states.

Other targeted goods include motorcycles, farm equipment and appliances. Milwaukee-based Harley-Davidson sold 6,400 motorcycles in Canada last year, about 5% of its worldwide total. John Deere and other manufacturers produce farming equipment throughout the Midwest, including in Illinois, Iowa and Wisconsin. Appliance production is concentrated in Ohio and Kentucky.

Where did the U.S.-Canada trade relationship stand before this latest tension?

President Trump began his second administration with a volley of tariffs against Canada, saying they were punishment for illicit fentanyl entering the U.S. Those were later struck down by the Supreme Court. He also imposed separate levies on imports such as steel, aluminum, lumber and autos that still stand. Canada last year issued retaliatory tariffs on American-made autos and metal products, and some Canadian provinces have banned U.S. alcohol sales.

In July, the U.S. declined to renew the U.S.-Mexico-Canada free-trade agreement in its current form, launching an annual review process and the latest round of friction.

Could the latest tension escalate or cool off?

The Canadian measures don't take effect until Sept. 8, and an even more punishing tariff response that Trump threatened on Monday-imposing 50% tariffs on automobiles and parts from Canada-wouldn't take effect until January. So there is time for both sides to "gauge what the costs are and maybe find alternative solutions," said Jeff Schott, a trade expert at the Peterson Institute for International Economics.

Rhetoric on both sides has grown increasingly heated, however. "Last spring, I warned that America is trying to break us so they can own us and I promised that that will never, ever happen," Canadian Prime Minister Mark Carney said on Saturday. "We are keeping that promise. Canada is becoming stronger and less dependent on America."

One legal avenue for the U.S. to justify escalation: the clause Trump used to impose his Aug. 22 tariffs on Canada-section 338 of the Trade Act of 1930-allows the U.S. to ban goods from countries that retaliate against such tariffs, according to Barry Appleton, co-director of the Center for International Law at New York Law School.

This explanatory article may be periodically updated.