US Vice President Mike Pence looks at North Korea from the border village of Panmunjom on April 17, 2017. Pence visited a military base near the Demilitarized Zone, a day after the North conducted a failed missile launch. Pence arrived at Camp Bonifas on Monday for a briefing with military leaders and to meet with American troops. He is in South Korea as part of a 10-day tour of Asia. Lee Jin-man/AP

US President Barack Obama looks toward North Korea from Observation Post Ouellette during a visit to the DMZ on March 25, 2012. Obama arrived in Seoul earlier in the day to attend the Seoul Nuclear Security Summit. SAUL LOEB/AFP/Getty Images

US Vice President Joe Biden and his granddaughter Finnegan Biden visit the DMZ on December 7, 2013. In addition to South Korea, Biden also visited Japan and China to discuss the Trans-Pacific Partnership, the South China Sea, economic relationship with China and the implementation of the US-Korea Free Trade Agreement. Chung Sung-Jun/Getty Images

US President George W. Bush looks at North Korea from Observation Point Ouellette in the DMZ on Feb. 20, 2002. The president visited the zone to express his hope for communist North Korea to rejoin democratic South Korea someday. J SCOTT APPLEWHITE/ASSOCIATED PRESS

US President Bill Clinton surveys the North Korean border on his tour of the DMZ during a post-G7 summit trip in July 1993. Diana Walker//Time Life Pictures/Getty Images

US President Ronald Reagan looks across the DMZ at Guard Post Collier, South Korea, on November 13, 1982. David Hume Kennerly/Getty Images