North Korea is firing up one of its nuclear reactors, and likely producing weapons-grade plutonium for nuclear weapons, according to a new report from the International Atomic Energy Agency. The agency says North Korea appears to have stopped refining plutonium for years — notably during talks with former President Donald Trump. The agency says the fact that reactors are up and running again is “deeply troubling.” The World’s correspondent in Asia, Patrick Winn, has been following this story.