An ultra-conservative Iranian cleric who opposes all dialogue with the West is a frontrunner to become the country's next supreme spiritual leader.In a move that would push Iran even further into the diplomatic wilderness, Ayatollah Mohammad Taghi Mesbah-Yazdi, 71, who publicly backs the use of suicide bombers against Israel, is campaigning to succeed Grand Ayatollah Ali Khameini, 67, as the head of the Islamic state. Considered an extremist even by fellow mullahs, he was a fringe figure in Iran's theocracy until last year's election of President Mahmoud Ahmadinejad, a fellow fundamentalist who views him as his ideological mentor. He is...