Iran’s top nuclear negotiator was heading back to Tehran on Sunday to consult with his nation’s leadership, as negotiators remained divided over how to limit and monitor Tehran’s nuclear program and even on how to interpret the preliminary agreement they reached two months ago.

David Sanger, senior fellow at the Belfer Center and adjunct lecturer in public policy at Harvard Kennedy School, was interviewed on NPR’s “On Point” about his new book on President Obama’s foreign policy efforts, including a cybercampaign against Iran’s nuclear program. Sanger’s book, Confront and Conceal: Obama’s Secret Wars and Surprising Use of American Power, was published this week.