It's been five years since the U.S. pulled out of the nuclear deal. What followed: the U-S re-imposed crushing sanctions, over time, Iran stopped adhering to the limits the deal had set and day-by-day its nuclear program crept forward.So how close is Iran to a bomb? What can the U.S. do to stop Iran, if it chooses to pursue one? And how are regional and global shifts changing the equation?NPR's Mary Louise Kelly puts these questions to the U.S. special envoy for Iran, Rob Malley, and to Vali Nasr with the Johns Hopkins University School of Advanced International Studies.In participating regions, you'll also hear a local news segment to help you make sense of what's going on in your community.Email us at considerthis@npr.org.