The Trump administration has sent a message to the world with its new tariff threats against Mexico: No deal is ever a done deal.

That effect may be bigger than the immediate 5 percent tax on Mexican imports set to go into force June 10 and escalate to 25 percent over time.

Mexico had seemed to resolve its trade tension with the United States, in the form of a reworked Nafta now known as the United States-Mexico-Canada Agreement, or the U.S.M.C.A. The deal was moving toward fruition after the United States lifted steel and aluminum tariffs on its North American neighbors just days ago, and lawmakers in all three countries began considering it.

The new tariff threats, announced by President Trump in a tweet on Thursday, are aimed at pressuring the Mexican government to do more to combat migrants traveling from Central America to the U.S. border to seek asylum. It’s an issue not really related to trade policy at all. But the tariff threats amount to a vivid signal, especially to allies, that there is no permanent trade peace with the Trump administration, and could have significant consequences for future trade negotiations.