this is obviously a kind of a freudian slip. he misspoke because he forgot that bush wasn't in office anymore - the eight years were meant to apply to bush, and then he remembered that obama existed and tried to save it. he should have just admitted it. that's a common theme with bill: why don't you just admit it, man? smoking pot. banging secretaries. forgetting that obama ever happened. but, that's why this slip is freudian: in the long run, obama and bush may very well blur together into a single historical term. obama is, historically, just a continuation of bush. it's not what he consciously meant to say, but it is what he subconsciously knows is true. oops.