What the rotund Congresscritter from my home state (but a whole bunch south of me!) doesn't seem to understand is this: What goes around, comes around. As you want to investigate, so shall you (or your side) be investigated--and treated far worse than you treated those who "perpetuated the 'crimes.'"
Obama seems to understand this. He makes noises in the directions that the 'bats want him to go, but it is highly likely that said administration has committed offenses already that would result in felony convictions, so he doesn't want to set a precedent by which David Axelrod, Rahm Emanuel, Robert Gibbs, or anyone else in his administration would be prosecuted (and sent to Marion, Illinois, or Leavenworth, Kansas, to name two maximum security Federal prisons) by a future administration. Because it would happen.