The downing of a Chinese spy balloon earlier this month was the first in a series of incidents in North American skies. WASHINGTON — The U.S. government and Canada have been busy intercepting unidentified flying objects in the skies, shooting down one on Friday over Alaska, another on Saturday over the Yukon Territory and a third over Michigan on Sunday. White House officials said on Monday that the military had not yet identified the source of the objects or their purpose, adding that there was no indication that civilians on the ground were in danger and that the government would...