TOPSHOT - US President Barack Obama (R) speaks with Sheikh Mohammed bin Zayed al-Nahyan (L), Crown Prince of Abu Dhabi, during the US-Gulf Cooperation Council Summit in Riyadh, on April 21, 2016.
Obama met Gulf leaders in Saudi Arabia to push for an intensified campaign against the Islamic State group, despite strains in Gulf ties with Washington.

 / AFP / Jim Watson        (Photo credit should read JIM WATSON/AFP via Getty Images)