Early Office of Force Transformation brief slide. Probably 2002.
Simple point WRT Core-Gap divide: no one was/is talking preemption anywhere in the Core--only in the Gap. In the Core, it's a world of "assurance" among allies and--at worst--frenemies. Between the two there are some efforts at suppression of bad flows (e.g., pandemics from Gap to Core) and some deterrrence (missile shields to protect Core from rogues like Iran).
Just another way of saying that what Bush-Cheney was pushing in terms of perceived radical departure from the past was delimited to the Gap, where the ideas were--and remain--not all that radical.
Bottom line on slide: point being, the rule-set against preemption pretty clear across Core, but Core's stability and connectivity and rule-sets do not extend everywhere, so argument for preemption simply admits that there are still places beyond the stable frontier where rules find little purchase.