A problem dysfunctional societies have always had (pretty much) is that the party in power uses the levers/hammers of power to smash the party/parties that are currently out of power. Once the opposition loses power, its members wind up in jail - or shot. Think of Trotski with that ice pick in his head down in Mexico. Then again, what goes around comes around. It will be their turn next time. The shoe will be on the other foot sooner or later.
Many on this site are eager to nail criminality. Good. It is a problem, however, if the DEMs (Power) starts going whole hog after the GOP (Out of Power) with the sort of abandon that many on Daily Kos demand. What appears to the DEMs as "Justice!" may very well be the same old, same old. Bash those out of power.
President Obama's administration is smart when it is extremely careful about going after Bush Junior's disdeeds/crimes - and Junior to was the worst president in a lifetime, perhaps ever. Barack Obama just got back from Africa and gave a speech about the importance of good governance. How many African governments in recent years spent too much effort clobbering their opposition and not enough time providing good government? Lots.
Eric Holder has a duty, as AG, to investigate crimes. Cheney was a poisonous reptile much of the time, apparently. Where to start? It's a target-rich environment for prosecutors. Yes, the GOP didn't hesitate to launch as many investigations of the Clintons as they could think up, including impeachment.
But the GOP hates government - if the public reaches the same conclusion then the GOP would be overjoyed. An ugly, vengeful government serves the GOP ends. If Americans end up hating their government, then it is party time for the Republicans.
The DEMs need government - it is the only instrument there is to hold private power in check and provide services that neglected people need. Unlike the GOP, DEMs don't want the public to hate government. Will a series of criminal investigations of Bush Junior's gang produce an admirable cleaning-up of our system as we all want? Or will it end up coming across in the public mind like powerful people/entities pounding their foes just because they can?
Barack Obama is class act. He wants to do it right. He wants to make this a better place. And he knows, most likely, what a minefield these investigations of past administrations can be. And that the next GOP administration can easy set up an "Investigation of the Obama Administration" team and go to town.