WASHINGTON — Escalating blockades at the Canada-U.S. border are weakening one of the most fragile links in the vital North American supply chain — a link that has nothing to do with transport trucks, highways or bridges.

Rather, it's the mood in the United States, particularly when it comes to issues like globalization, international trade and making things in America, that may pose the biggest danger over the long term.

Michigan Rep. Elissa Slotkin is angry that a General Motors plant outside Lansing is cutting shifts, starved of auto parts from Canada by the ongoing closure of the border crossing between Detroit and Windsor, Ont.

Her politically charged solution is the sort of thing that keeps Canadians up at night.

"It doesn't matter if it's an adversary or an ally — we can't be this reliant on parts coming from foreign countries," Slotkin tweeted Wednesday.

"The one thing that couldn't be more clear is that we have to bring American manufacturing back home to states like Michigan. If we don't, it's American workers like the folks at Delta Township who are left holding the bag."

She doubled down Friday, urging Canada to end the blockades before vowing "to continue the work that Michiganders have been pushing for over the last 30 years: bringing manufacturing of critical items back to the U.S. so we're not dependent on others for our economic security."

It's hardly a new sentiment. U.S. protectionism has been a fact of life, off and on, for decades. But even a year removed from Donald Trump's turbulent turn as president, it's very much on — thanks in large measure to Trump's successor.

And with Republicans anticipating a romp in November's midterm elections, embattled Democrats will take all the working-class talking points they can get.

"They'll use American parts, American iron, American steel," President Joe Biden gushed earlier this week as he announced Australian manufacturer Tritium's plan to build electric vehicle charging units in Tennessee.

"I made it clear from Day 1: when the federal government spends taxpayers' dollars, we're going to buy American: American products made in America, including American component parts."

Biden and Justin Trudeau spoke by phone Friday about the crisis, White House press secretary Jen Psaki said in a statement that suggested the prime minister got an earful from the U.S. commander-in-chief.

"The president expressed his concern that United States companies and workers are experiencing serious effects, including slowdowns in production, shortened work hours and plant closures," Psaki told the daily briefing.

"The prime minister promised quick action in enforcing the law."

Canada's not especially fussed about Biden's specific Buy American policies when it comes to federal infrastructure projects; it has negotiated carve-outs to those rules before, most recently under Barack Obama in 2009.

But experts warn that the drumbeat of protectionist rhetoric has an effect over time, particularly at the state and local level, where Canadian suppliers and contractors potentially face a more serious threat.

"The blockades not only strike against the rule of law that protects our rights and freedoms, but also undermine Canada's international reputation," business leaders wrote Friday in an open letter released by the Canadian Chamber of Commerce.

"We are already hearing calls to move investment, contracts and production from Canada because of our inability to guarantee timely delivery to international customers."

Nor is it as simple as finding alternative customers and suppliers, warned Maryscott Greenwood, CEO of the Canadian American Business Council.

"The big risk and danger of the border uncertainty is that the Canada-U.S. economic relationship is one organism — you can't say, 'Well, we don't really need the heart, because we've got the lungs,'" Greenwood said.

"We have to get back to the point where the two countries together are figuring out how to keep the patient healthy."

Whatever the ailment, the symptoms — already familiar to Americans — are about to manifest themselves south of the border once again.

The White House, growing more seized by the day with the magnitude of the crisis, is urging Ottawa to use "federal powers" to end the blockade and bracing for similar protests to materialize at Sunday's Super Bowl in Los Angeles.

On right-wing social media and chat platforms like Gab and Gettr, talk is coalescing around plans for a similar "convoy" protest that would begin in California early next month before making its way to D.C. There is also scattered talk of trying to disrupt Sunday's Super Bowl in Los Angeles.

But in a country like the U.S., which is far more culturally and politically divided than Canada, the two sides are more evenly matched.

"It'd be great," firebrand Kentucky Sen. Rand Paul said Thursday in an interview with the conservative Daily Signal website as he encouraged protesters to "clog up" U.S. cities.

"It'd be a nice change; we'd actually have some traffic."

White House officials say they have no evidence to suggest anything nefarious or criminal is in the works, and that their principal focus for now is clearing the border blockades.

Homeland Security Sec. Alejandro Mayorkas and Transportation Sec. Pete Buttigieg have been in regular touch with their Canadian counterparts, Public Safety Minister Marco Mendicino and Transport Minister Omar Alghabra.

Liz Sherwood Randall, the White House national security adviser, also spoke late Thursday with Jody Thomas, Justin Trudeau's national security and intelligence adviser, officials in the Prime Minister's Office confirmed.

The auto-sector ties between Windsor and the U.S. are too strong, having been forged over more than a century, to be severed by a "singular event," said Flavio Volpe, president of Canada's Automotive Parts Manufacturers' Association.

But the longer-term effects of a protracted border shutdown could be costly, Volpe told a news conference Thursday as stakeholders in Windsor sought a court injunction to end the protest.

"I do think If we don't take some action here … to clear the border, I think it may have some effect at least in the short to mid-term on whether new investments would favour Windsor over the other side of the bridge."

A hearing on the injunction was underway Friday in Windsor, the same day Ontario Premier Doug Ford declared a state of emergency and promised "severe" consequences for those who refuse to disperse.

Rakesh Naidu of the Windsor Chamber of Commerce said he's worried that if they continue much longer, the protests will have a chilling effect on U.S. enthusiasm for investing in and working with Canada.

"The concerns that we have are, what will the American customers, the American clients, think of the situation and will this lead to them rethinking the supply chain that extends into Canada," Naidu said.

"The American customers may look the other way and not want to have a concern like this come up in the future."

This report by The Canadian Press was first published Feb. 11, 2022.

James McCarten, The Canadian Press