The minister of the economy, Mr. Guajardo Villarreal, argues there is little point for Mexico to respond now to Mr. Trump’s threats to wall off the Mexican people and slap a 35 percent tariff on Mexican imports. “We must not overreact to campaign rhetoric,” he told me. Still, the truck story suggests the Mexican government understands that it needs a contingency plan in case Mexico’s most important partner on the world stage were to suddenly turn hostile.

The outline of a strategy seems clear: Mexico must communicate to the United States just how valuable their relationship is, and how self-destructive it could be to undermine it. The question is how to make this case. How persuasive can Mexico be?

A slide from a presentation that Mr. Guajardo Villarreal and his aides carry with them as they speak to American business and political leaders shows what the 2017 Ford Fusion, made in Hermosillo, in northern Mexico, would cost if a 35 percent tariff were imposed on imports from Mexico: $30,253, which is almost $8,000 more than it costs now. Another slide shows that eight of 10 avocados consumed in the United States are grown in Mexico, as are nine of 10 limes and half of all tomatoes.

Six million American jobs also depend on exports to Mexico, one slide says. Mexico buys nearly $250 billion worth of stuff from the United States. And 37 cents out of each dollar’s worth of Mexican exports to the United States came from the United States in the form of parts and other components. “If you throw obstacles at the relationship with Mexico, you would be shooting yourself in the foot,” Mr. Guajardo Villarreal told me.

Allies in the United States would indeed help Mexico make its case, including states and municipalities that would be hurt by Nafta’s unraveling, and businesses that would be forced to relocate production and rethink their global supply chains.

But perhaps a more muscular approach is needed. Jorge Castañeda, a former Mexican foreign minister who is a harsh critic of Mr. Peña Nieto, suggests that Mexico’s best argument is that the country’s stability and prosperity are indispensable for the national security of the United States. Americans worried about illegal immigration across the southern border might stop to consider what it could look like if the Mexican economy went into a tailspin.