Former central banker Mark Carney will become Canada’s next prime minister after the governing Liberal Party elected him its leader as the country deals with U.S.

Carney, 59, a political novice, will take over at a tumultuous time in Canada, which is in the midst of a trade war with the United States.

The president signed executive orders today offering a monthlong exemption, until April 2, for all goods covered under the U.S.-Mexico-Canada trade agreement, which includes most U.S. imports from those countries. About 10 percent of Mexico’s exports to the U.S. fall outside the U.S.M.C.A. trade agreement, according to one economist.