FILE - In this Feb. 21, 1972, file photo, Chinese communist party leader Mao Zedong, left, and U.S. President Richard Nixon shake hands as they meet in Beijing, China. The notion of a substantive sit-down between North Korean leader Kim Jong Un and U.S. President Donald Trump ‚Äì the most gazed-upon figures of this moment in the planet's history ‚Äìis a staggering prospect and a potential logistical nightmare if the two countries ever tried to make it happen. (AP Photo, File)