What keeps the head of the UN's nuclear watchdog up at night? It's not only Vladimir Putin threatening to use a tactical nuke in Ukraine.

Weeks ago, International Atomic Energy Agency chief Rafael Grossi witnessed first-hand how close we came to another Chernobyl disaster thanks to fighting near the Zaporizhzhia nuclear power plant in southern Ukraine. And then there's Iran, on the cusp of getting the bomb, and North Korea, a rogue state amassing an entire arsenal of nukes.

On GZERO World, Ian Bremmer asks Grossi about the world's nuclear threats and what the IAEA is doing about them. Grossi views himself as a mediator — if leaders are willing to listen to him.