Amir Taheri writes that Ahmadinejad may very well be the most unwelcome guest in Iran: FOR 30 years, the tradition has been for each newly elected president of the Is lamic Republic to travel at once to Mashad, Iran's main "holy" city, to thank Ali bin Mussa, the only one of Shiism's 12 imams buried in Iranian soil. When he was first elected president four years ago, Mahmoud Ahmadinejad made