Obama in Riyadh: Are the US and Saudi Arabia still allies?

Barack Obama has met with Gulf leaders in Saudi Arabia to discuss the state of the Middle East. The wars in Syria and Yemen, and the fight against jihadists were all on the agenda, as was Iran. But one question looms larger than the rest: are America and Saudi Arabia still friends? For 70 years they've been allies: Riyadh sold oil, Washington provided security. But yesterday, when the US president landed in Saudi Arabia, King Salman was conspicuously absent from the welcome party.