The idea of tightening trade rules to encourage more manufacturing in the United States obviously plays well with voters. Republican presidential front-runner Donald Trump, in particular, has found surprising success attacking trade deals such as the North American Free Trade Agreement while claiming, “We’re losing so much with Mexico and China,” because of U.S. trade deficits with those countries.

It makes for effective campaign rhetoric, but if Trump were ever to undo elements of NAFTA or impose punitive tariffs on Chinese products, it could cause havoc for a lot of American companies, and automakers in particular. “What’s important for our business going forward is we continue to open up our products to other markets,” Ford (F) CEO Mark Fields tells me in the video above. “Free and fair trade is really important. We have always supported every free-trade agreement since we’ve been in existence.”

Fields didn’t mention Trump by name, but Trump has singled out Ford as one company that benefits from lower manufacturing costs in Mexico. Ford has three plants in Mexico, where it builds cars such as the Fusion and Fiesta. But it’s hardly the only one. General Motors (GM) has four Mexican plants (vehicles built there include the Chevrolet Trax and Aveo), Fiat Chrysler (FCAU) has three (Dodge Journey, Fiat 500), Nissan (NSANY) has three (Versa), Honda (HMC) has two (CR-V, Fit), and Volkswagen (VOW.BE) has two (Beetle, Jetta, Golf). Manufacturers typically cluster in low-cost countries because once one company sets up shop, others must match the lower cost or end up at a competitive disadvantage.

Each of those automakers also employs thousands of Americans at U.S. plants. Most of them have factories in Canada as well. And GM this year will start importing a crossover from China, the new Buick Envision -- the first mainstream vehicle from China that will be sold in U.S. showrooms.

Automakers are about as global as global companies get, since the Big 7 – GM, Ford, Fiat Chrysler, Toyota, Nissan Renault, Honda and Volkswagen – operate on every continent. Where possible, they manufacture products close to where they sell them, to cut down on transportation costs and limit vulnerabilities stemming from to exchange-rate fluctuations. But they also seek low-cost opportunities wherever they can, especially for smaller vehicles that are hardest to make a profit on.

Many economists view the pivot toward protectionism as dangerous, even if concerns about the scarcity of good American jobs are real. For the auto industry, trade wars prompted by sharp hikes in U.S. tariffs on imports could upend global supply lines that took decades to put in place. Ford, for instance, exports its Explorer — which is built in Chicago — to more than 90 countries, and if the U.S. imposed new tariffs on imports from some of those countries, they would likely do the same to imports from the States. Ford would have to find a way to build the vehicle someplace where new tariffs wouldn’t apply, or give up such exports altogether.