Tourists walk next to a poster of Cuban President Raul Castro and US president Barack Obama in Havana, on March 18, 2016. US president Barack Obama touches down in Havana on Sunday to cap a long-unimaginable rapprochement with Cuba and burnish a presidential legacy dulled by Middle East quagmires and partisan sniping. As Air Force One rolls to a stop, Obama will become the first sitting US president to visit Cuba since Calvin Coolidge arrived on a battleship in 1928, before the discovery of penicillin or invention of the ballpoint pen.      AFP PHOTO/YAMIL LAGE / AFP PHOTO / YAMIL LAGE        (Photo credit should read YAMIL LAGE/AFP via Getty Images)