The race to become the next leader of the United Nations moved into a higher gear with the four declared candidates facing hours of questions over two days. Top among them: can the UN be made effective again? Rafael Grossi, an Argentine diplomat who heads the International Atomic Energy Agency, struck a downbeat note about the global body’s future during his interview replace Secretary General Antonio Guterres. “This election, or selection, process is so consequential, and this is because we are...