For almost a decade, Arab regimes have worried about alleged Iranian plans to create a "Shiite crescent" from the Persian Gulf to the Mediterranean, encompassing Iraq, Syria, Lebanon and a yet-to-be liberated Palestine. Now fresh fears have grown that the "crescent" may take another shape as well -- from the Persian Gulf to the Gulf of Aden, and including chunks of Saudi Arabia and Yemen. Since January, for instance, Iran has intensified pressure on Bahrain, where a Shiite majority has grievances against the Arab Sunni ruling elite. An archipelago connected with the Saudi mainland by a bridge, Bahrain provides the...