Canadian, Mexican and U.S. government officials and industry representatives, gathered here for the seventh negotiating round, were sent scrambling when Trump announced plans to levy tariffs of 25 percent on steel imports and 10 percent on aluminum imports to protect U.S. national security interests.

While negotiators have continued to meet, the tone has changed as Canadian and Mexican representatives try to figure out the impact on their countries and whether their leaders will retaliate if Trump doesn’t backtrack.

“Why are we signing a trade deal with a country that would unilaterally decide to restrict certain sectors?” said Jorge Guajardo, a former Mexican ambassador to China who now works as a senior director at McLarty Associates in Washington.