King Salman of Saudi Arabia has withdrawn from a carefully orchestrated summit with the US that President Barack Obama hoped would assuage Gulf anxieties about the conclusion of a nuclear agreement with Iran. Until Sunday the monarch had been expected to join other heads of state from the six Gulf Cooperation Council (GCC) countries at an unprecedented meeting at the White House and a day of talks at the presidential retreat at Camp David. Now the only leaders attending will be the emirs of Qatar and Kuwait. The summit, scheduled for Wednesday and Thursday, follows months of tension and intensive...