LAREDO, Texas —  Donald Trump’s only visit to the U.S.-Mexico border while running for president was a stop in Laredo that lasted less than three hours. On some days, that’s not long enough for 18-wheelers hauling foreign-made dishwashers and car batteries to lurch through the gridlocked crossing.

Trump’s campaign promise to tear apart the North American Free Trade Agreement helped win over Rust Belt voters who felt left behind by globalization. But the idea is unnerving to many people in border cities such as Laredo and El Paso or Nogales in Arizona, which have boomed under the 1994 treaty.

About 14,000 tractor-trailers cross the border daily in Laredo, the nation’s busiest inland port. Local officials say roughly 1 in every 3 jobs benefits from international trade.

“We are NAFTA on wheels,” Mayor Pete Saenz said.

Free trade across the border, he explained, is the “backbone” of this city of 255,000 people. The Democrat endured a backlash from his party for welcoming Trump in July 2015 after the then-candidate called immigrants from Mexico criminals and rapists.