As “Countdown to Zero” producer Lawrence Bender discovered, making a movie about nuclear weapons isn’t exactly easy. Most people don’t think about them, and those who do don’t necessarily want to talk, Bender explained. Still, Bender and director Lucy Walker secured commentary from an impressive catalog of world leaders, some of whom had to be booked over a year in advance — from former Pakistani President Pervez Musharraf to former Russian leader Mikhail Gorbachev to former British Prime Minister Tony Blair. Though they all agreed that the ideal number of nuclear weapons in the world is zero, Bender found, getting to zero is a major political challenge. Bender stopped by Zócalo’s offices before Zócalo and KCRW’s screening of “Countdown to Zero” to talk about why the world is more dangerous today than it was during the Cold War, and what we can do about it.