The arrest of American journalist Roxana Saberi exposes Iran’s Achilles heel, a weakness so fatal that it might one day lead to the downfall of the Islamic Republic. Saberi, who has worked as a freelance journalist in Iran and elsewhere in the Middle East for the last six years, has been accused of spying for the United States, a charge that can carry the death penalty if she is convicted. But Saberi’s profile hardly fits that of a typical espionage agent. A former beauty queen who held the Miss North Dakota title and was a top-10 finalist in the Miss America pageant, Saberi double majored in French and communication at a small-town college in Minnesota.