The National guitarist and composer discusses the making of his new Big Red Machine record with Bon Iver's Justin Vernon, 'How Long Do You Think It's Gonna Last,' which features appearances by musical friends like Fleet Foxes, Anaïs Mitchell, Sharon Van Etten and Taylor Swift. He also opens up about what it's like to win an Album of the Year Grammy (for his work on Swift's 'folklore'), his love for the Grateful Dead, and how it feels to sing his first set of lead vocals — at age 45!