Japan is hosting its fellow G-7 partners — Canada, France, Germany, Italy, the UK and the US — in Hiroshima, the site of one of the only two nuclear attacks in history. Three of the G-7 members are also nuclear powers. Host Marco Werman speaks with James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, about the state of nuclear nonproliferation today, against the backdrop of a proposed resumption of nuclear testing by North Korea and the implied threat of the use of tactical nuclear weapons by Russia in Ukraine.