Barack Obama arrives in Saudi Arabia’s capital, Riyadh, today to meet King Salman, who ascended to the throne on the death of his half-brother, Abdullah, on Friday. (Most visiting world leaders came over the weekend to present their condolences.) Saudi Arabia and America, allies since 1945, have shared interests in counter-terrorism and stability: America has Saudi Arabia’s back in the region; the kingdom sells America oil and buys its arms. But the two countries have their disagreements: Saudi Arabia feels let down by America’s lack of will to oust Syria’s Bashar Assad and worries about the ensuing expansion of Islamic State and the increasing influence of Iran. Usually tight-lipped American officials, for their part, have recently been pushed into condemning the flogging of a Saudi blogger who called for more freedom of expression. Tensions are showing in an old partnership.