"The paradox wouldn’t last. Iran and Saudi Arabia both feared ISIS, but they hated each other more. Secretly, many Arabs cheered ISIS on, hoping it would bring Tehran to its knees and put an end to Iranian dreams of hegemony in the region. And as Iran took the lead in fighting ISIS on the ground, it looked like Shias were out to kill any Sunnis, the latest brutal, sectarian mutation of the Saudi-Iran rivalry. Which came first: Iran’s imperial sectarianism or the Sunni sense of exceptionalism? By now the dynamic was hard to unpack, but it was about to intensify with the rise of King Salman and his favorite son, prince Mohammad bin Salman. While Obama dismissed Iran’s “destabilizing activity” as a “low-tech, low-cost activity,” Saudi Arabia watched with alarm as Iran poured thousands of men and an estimated $35 billion into Syria to prop up Assad. Suleimani was turning into the king of Iraq. As the US-Iran nuclear negotiations inched closer to a deal in the spring of 2015, the Saudis grew unnerved by the prospect of cash flowing into Iran’s coffers after the lifting of sanctions. They seethed as US secretary of state John Kerry and the Iranian foreign minister Javad Zarif exchanged pleasantries and smiled for the cameras during the negotiations."