The Ambassador Bridge soared over the split rivers of Detroit and Windsor in Ontario, a symbol of economic and cultural relations that constrained sister cities across the international border.

The crossing point is one of North America's busiest people, moving about $400 million in freight every day across the bridge. Nearby, more than 3.9 million vehicles crossed the Windsor Tunnel in Detroit last year - some went to work, some headed to concerts, sporting events or favorite restaurants.

But the trade policy of U.S. President Donald Trump puts these historic links under pressure. Tariffs and related uncertainties undermine the prosperity of the region and wear down descriptions of government, business and labor leaders using words such as “family” and “best friend.”

"It's a boundary of existence, but it's not a cultural issue," said Ryan Donally, CEO of the Windsor Essex Chamber of Chamber. "So, for this trade war, it's even more painful to start breaking down the social structure between Detroit and Windsor because frankly, it's not just business. It's not just taxation. It's hurting the cultural relationship between two best friends."

Trump's tariff plan suffered a setback Wednesday, with a court ruling declaring invalid and conclude that the president exceeded his mandate. Washington's appeals court temporarily suspended the decision Thursday - which did not affect certain trade restrictions between the United States and Canada, including tariffs on cars - a key link between Detroit and Windsor.

In this place, the place where winter freezes are described in Celsius and Fahrenheit summer candy. The Detroit Lions’ American football team here includes the Ontario postal code, limiting ticket sales to hometown fans, while the route of the Marathon in Motor City crosses the bridge and returns through the tunnel. Everyone knows that someone gets married at the border.

The automotive industry is probably the most critical economic bond between Detroit and Windsor. Stellantis built Dodge Charger and Chrysler Pacifica at the Windsor factory. Ford builds nearly 2,000 engines every day in Windsor Daily that enter the best-selling F-Series trucks assembled in Kentucky and Michigan.

Unifor Local 200 President John D'Agnolo represents 2,000 workers at the Ford Engine Factory. The company sent a letter to workers this month that does not expect any changes in the factory.

Despite this, the uncertainty is obvious. Dagnolo said Canadians buy more Ford cars than they do. He added that if Ford closes factories in the country, many Canadians will not buy cars and trucks, which means cutting "thousands of jobs" in the United States.

The North American automotive industry is so integrated that it moves across borders many times as the vehicle is assembled. This stings Trump's rhetoric attack on Canada. "It breaks your heart when you hear him talking like they don't need us," D'Agnolo said.

Trump's 25% tariff on cars has led to Canadian layoffs, even under the US-Mexico-Canada trade agreement for preferential treatment for vehicles. Louis Jahn, owner of the Jahn engineering company and head of the Canadian Tooling & Machine Association, cut his 70 employees by 20% as orders for U.S. automakers dries. Some of the association's approximately 200 members fired half of its workers.

Jahn Engineering also paid more for certain components it imported from the United States to make large tools for manufacturers due to Canada's retaliatory tariffs.

Jahn said the company passed on tariff fees to customers. “In the end, consumers will pay the price.”

In the U.S. in the Detroit River, tariffs present opportunities and challenges to Lisa Lunsford, CEO of Global Strategic Supply Solutions. Since March, manufacturers in suburban Detroit have cited more work as automakers and their suppliers try to source more parts and materials from the United States.

But uncertainty can also plague GS3. The company agreed to use Stellantis plans to be used on vehicles to be built in the Windsor factory in the future. When Lunsford learned that Stellantis had briefly idle the Windsor factory due to tariffs, she was concerned about the plan and the GS3's place. "It can still happen," she said. "But we don't know."

The pain in the United States will be more than limited to the automotive supply chain. Sandy Baruah, CEO of the Detroit Regional Commission, said GM workers benefited from a profit-sharing agreement that relies on profits from global procurement.

“Based on the trajectory we are ongoing, will GM workers get a $14,000 profit sharing this year?” he said. "No."

The economic impact exceeds the automotive industry. Baruah notes that about 6,000 workers cross the border every day, working in hospitals and doctors’ offices in Detroit.

Windsor-Detroit Tunnel Corporation CEO Tal Czudner said that compared with the same period last year, there were fewer vehicles passing through the tunnel, but the number of people fell by 18%. The difference shows that while commuting traffic remains stable, more families and friends over the weekend have crossed the border for leisure.

He said the time required to pass the checkpoint has also been extended as security measures have been strengthened.

Windsor Mayor Drew Dilkens also vetoed a measure to continue funding popular hourly bus services between cities. The Canadian federal government's legislation changes pushed buses from a carriage to a $1.4 million deficit, and Delkens said Trump's remarks made it impossible for him to ask taxpayers to fund it.

"We feel like we are under attack by the President of the United States," he said.

Transportation was also affected, with Windsor Port CEO Steven Salmons noting that the port’s number declines, usually around 5m tonnes per year.

Salmons said three steel shipments were cancelled in mid-March because the deal was reached before the tariffs, shippers worried that customers would not accept higher prices. Typically, steel can travel to three Detroit auto factories in Ohio, Michigan and Indiana.

Salmons said the salt transport is also "less" in American cities such as winter treatment roads such as Chicago. Salmons said next month, when cities start buying, they may face shortages and higher prices. Meat prices may also rise as less canola seeds are shipped to Toledo, Ohio for cattle and chickens.

In the first four months of the year, about 20% of trucks crossed the Ambassador Bridge, and even a few miles away workers approached the building of a new bridge, named after hockey legend Gordie Howe, a Canadian who played on the Detroit Red Wings for 25 seasons.

The bridge is scheduled to open in the fall, and local leaders say they expect relationships across the border to return to normal over time.

“We are our best friends,” Kudner said. “We still want to be our best friends and be optimistic, we will be back there.”