The government asks the forbidden question: How closely related is Islamic terrorism to mainstream Islam itself? Washington's policy-makers have been careful in the war on terror to distinguish between Islam and the terrorists. The distinction has rankled conservatives who see scarce difference. A little-noticed speech by President Bush in October gave them some hope. In a major rhetorical shift, he described the enemy as "Islamic radicals" and not just "terrorists," although he still denies that radicalism has anything to do with their religion. Now for the first time, a key Pentagon intelligence agency involved in homeland security is delving into...