It's not easy to remember that terrorists, too, are in politics, with all the insecurity and ambition that implies. Certainly that's true of the four famous Islamic killers, two of them dead, whose statements, distributed on the Web, fill Al Qaeda in Its Own Words (Harvard University Press), published this week. Their messages rally the troops and attempt to recruit new soldiers, but also read like the pleas of politicians for status within the loosely defined and always changing jihadist movement.