Since the revolution of 1979, Iran's political mood has cycled several times toward and away from upheaval. Now, the Islamic republic finds itself yet again on the brink.Pressure on the mullahs who run the country comes from several directions.Increasingly alarmed by Iranian efforts to develop nuclear weapons, external powers threaten to tighten trade sanctions against the defiant theocracy. France, in particular, has hardened its position."There is no longer any reason to wait," the country's ambassador to the United Nations, Gerard Araud, told the Security Council this month.His country, the US, and Great Britain have met resistance to toughened sanctions from the other perman...