HANOI, VIETNAM - MAY 23:  Posters of U.S. President Barack Obama in front of a barber shop on May 23, 2016 in Hanoi, Vietnam. U.S. President Barack Obama started his three-day visit to Vietnam on Monday, aiming to strengthen the strategic and economic relationship between both countries during the historic visit four decades after the Vietnam war.  (Photo by Linh Pham/Getty Images)