The collapse of the 1994 trade deal would reverberate throughout the global economy, inflicting damage far beyond Mexico, Canada and the United States and affecting industries as varied as manufacturing, agriculture and energy. It would also sow at least short-term chaos for businesses like the auto industry that have arranged their North American supply chains around the deal’s terms.

The ripple effects could also impede other aspects of the president’s agenda, for example, by solidifying political opposition among farm state Republicans who support the pact and jeopardizing legislative priorities like tax reform. And it could have far-reaching political effects, including the Mexican general election in July 2018 and Mr. Trump’s own re-election campaign.