...credit for a booming economy even though he had nothing to do with the current state of the union (or in the reverse, if the economy is bad he shouldn't be blamed for it starting day one on the job). There is a carryover from one presidency to the next and it takes time for one president to overcome the effect the previous one had on the economy. Eventually we'll reach a point where the current president can no longer blame the previous president for problems he has to deal with.
It's a little naive to think it can be so black and white when there's so much carryover from one regime to the next whether you're talking college football or any organization that doesn't clean house and start from scratch.