Saudi Arabia has cut diplomatic ties with Iran after the storming of its embassy in Tehran. The Iranians warn of "divine vengeance" over the New Year's execution of a prominent Shiite cleric, Nimr al-Nimr. Protests are raging all over the Muslim world. The crisis is occurring on the watch of a new king in Saudi Arabia, which has a sizable Shiite majority in its own land. How far will the escalation go?
