Observers with a working knowledge of Iranian politics have largely been able to shrug off President Mahmoud Ahmadinejad's bluster and bullying, knowing the diminutive President must still answer to a far more powerful figure: Supreme Leader Ayatullah Ali Khamenei. Since 1989, the shadowy cleric — a former president himself — has sat at the apex of Iran's complex hierarchy as the final word in all political and religious matters. The massive protests roiling Tehran in the aftermath of the June 12 elections have underlined both the vast sweep of Khamenei's powers and, perhaps, its limitations. After hailing Ahmadinejad's "divine victory," Khamenei backpedaled by ordering the country's Guardian Council to investigate the results — a decree that some took as an implicit capitulation to factions sympathetic to Mir-Hossein Mousavi, Ahmadinejad's challenger. In his two decades at the helm of the Islamic Republic, Khamenei's present challenge — to guide Iran through this stretch of turbulence while the world watches transfixed — may be his toughest yet.