In “The Secret History of the Credit Card,” correspondent Lowell Bergman surveys the credit-card industry to explore reasons why cards are so easy to get and hard to pay off. The hour examines issues like interest rates, data-sharing and the industry's clout in Washington, but the short answer, as Bergman puts it, is that “the most profitable part of the industry is when they get people into debt.” A coproduction with the New York Times.