OTTAWA—The Canadian military will begin wrapping up its mission at Kabul airport ahead of the Aug. 31 deadline the United States set for ending the mission, Defence Minister Harjit Sajjan said Wednesday. Sajjan said that’s because the United States is leading the mission and providing security and so its forces, some 6,000 personnel, must be the last to leave the airport. That means Canada’s special forces and aircrews must begin departure preparations in advance. Canada is using two C-17 transport planes to airlift Afghans to safety, and is one of 13 countries taking part in the airlift. It also has special forces operatives on the ground who are working outside the airport’s confines to spirit fleeing Afghans to waiting flights. “Drawing down a mission takes a considerable amount of time. It is not done overnight and it comes with considerable risk,” Sajjan said, but he declined to give specific details. …