A rationale, of course, is the logic behind some position or course of action. So the "logic behind the rationale" is the logic behind the logic behind some position or course of action—a concept I'm having trouble wrapping my mind around. Of course, if we adopt the more cynical sense of the word "rationale"—the purported but not actual logic behind a position—then Bush's phrase could have some actual meaning. For example: Maybe he explained to European leaders that behind the official rationale for missile defense—smacking down missiles launched by wacko leaders of rogue states—lie the actual goals of feeding the military industrial complex and keeping Donald Rumsfeld off the streets. But somehow I doubt it, even though one of those goals would indeed be laudable.