The things that probably keep Barack Obama up at night — terrorist networks, covert nuclear programs and chemical weapons — can often be countered with off-the-peg reasoning: drones, sanctions, inspections, or even the threat of intervention. Much more difficult is working out how to stop allies from destroying what he hopes will be the signature achievement of his second term: a historic opening to Iran. When it comes to the Middle East, Obama’s thorniest problems come not from his enemies, but from his friends.