Gary Johnson, the Libertarian Presidential candidate, was once a staunch advocate for legalizing marijuana. The former New Mexico governor joins David Remnick in a discussion about his new pot-free life, Social Security reform, and whether schoolteachers should have semiautomatic rifles in the classroom. Plus, the singer-songwriter Angel Olsen and Kelefa Sanneh listen to a track from Olsen’s latest album, “My Woman”; a curator at the American Museum of Natural History spiffs up a dead bee; the actor Reed Birney reads Donald Barthelme’s classic short story “The School”; and Joshua Rothman investigates our obsession with travelling to Mars.