MEXICO CITY — Vicente Fox, the former president of Mexico, was recently stuck in Mexico City traffic, overcome with frustration — not by the congestion, but by something that was irritating him even more: Donald J. Trump. He grabbed his phone, turned the lens on himself and pressed record.

“Ha! Donald,” Mr. Fox said, holding the phone perhaps a little too close to his face. “What about your apologies to Mexico, to Mexicans in the United States, to Mexicans in Mexico?”

In short order, the 15-second clip was on Mr. Fox’s Twitter feed — another salvo in a personal campaign against the American presidential candidate that has included television appearances, radio interviews and a fusillade of hectoring Twitter posts.

Mr. Fox’s voice is among a growing, if uncoordinated, chorus of influential Mexicans worried about what a Trump victory could mean for the complex relationship between the United States and Mexico — not to mention the impact Mr. Trump’s presidential bid may have already had.