It is not surprising that research is being done in to Eric Holder's actions while in the Clinton Administration. From an experience point of view, I think Holder is probably the most qualified Obama nominee for his job. While some of Holder's actions are probably not as dastardly as Republican operatives would have you believe, some of things are bothersome and require some sort of real explanation.
I don't know how and where to rank the pardon of Marc Rich in the scheme of Clinton Administration shenannigans, but it does reek of impropriety (although I will readily admit it was with the President's power to grant).
While this is clearly an attempt to create doubt as to Holder's fitness to be attorney general, it won't stop him. At this point only Holder or Obama can stop the nomination, because you can be sure that Holder's confirmation hearing will be a love fest from the left and a slug fest from the right and it will be all for show.