Great piece by Steven Metz on the outdated alliance with SA.
Here is one bit
Ironically, the rise of violent, transnational Islamist extremism, led first by al-Qaida and later by the Islamic State, both solidified the U.S.-Saudi relationship and amplified its fissures. While Riyadh never intended to create revolutionary movements like al-Qaida and the Islamic State, its aggressive efforts to spread its deeply conservative Wahhabist strain of Islam inadvertently set the stage for extremist ideologues like Osama bin Laden. Unlike the Soviet or Iranian threats, violent Islamist extremism emerged from within Saudi Arabia, as demonstrated by the fact that most of the 9/11 hijackers and many of the foreign fighters in the Iraqi insurgency were Saudis
The rest can be read here.