I do think that none of the agents I saw around Bush are on Obama's detail. My guess is that they were transferred in order to avoid a contrast between the two men in their observations.
Either that or they all put in for duty in Crawford, Houston, Dallas, or Kennebunkport.
I recall one SS agent who flashed a huge toothy smile at us while we were protesting Al Gore at a fundraiser. Made our day!
Maybe that fond memory is possibly the reason I’m wondering how far they go wrt loyalty.