Last week, after the Air Force shot down a Chinese surveillance balloon, examination of its wreckage revealed that it could not only take images, but also scoop up radio and cellphone communications. The balloon, the U.S. military said, was part of a bigger global program by China to collect information about military operations. Since then the U.S. has shot down three other objects from the skies over North America — apparently without knowing much about them. Guest: Julian E. Barnes, a national security reporter for The New York Times.