STORY: Earlier in the day, Biden also toured the Korean Air and Space Operations Center (KAOC) with South Korean President Yoon Suk-yeol, where U.S. and South Korean troops are tasked with defending any missiles the North might launch.On the second leg of his Asia trip, Biden will meet with leaders of Japan, India and Australia, a grouping known as the Quad, another cornerstone of his strategy to push back against China's expanding influence.