giants. the mission to save america's majestic sequoias. >> see you at the top. this is the "cbs weekend news." >> ninan: good evening. i'm reena ninan with the western edition of the broadcast. four more americans were killed today in afghanistan in a major breach of security. a suicide bomber blew themselves up inside the bagram airfield. that's the largest u.s. military base in afghanistan. the taliban claimed responsibility. over the past 15 years, the united states has spent about $115 billion in aid for afghanistan. thousand of american troops have given their lives. about 8500 remain. president-elect trump will soon become the third u.s. commander in chief to oversee u.s. military operations for a war with no end in sight. jonathan vigliotti has more from london. >> reporter: reena, afghan officials believe the suicide