Congress cannot prosecute the crimes of the Bush Cheney administration, in which the Department of Justice was involved. It's not their job, and its not Obama's job.  They can hold hearings and hope to get press on the issue, but only a prosecutor can hold criminals accountable.
The country needs a special prosecutor to investigate and prosecute the crimes of the administration, many of which seem to be admitted: FISA, torture, Hatch Act, Plame, DoJ hiring, Siegelman, etc.
For those of you incapacitated by the likes of loathsome Ken Starr, what level of crime would justify prosecution?  Wasn't it genius to trivialize the process?  Isn't it part of our self-hatred of a "government by the people" which Reagan started?  Remember the Republican mime-- we are the problem.
But just imagine if Bugliosi were the special prosecutor?  Now that would be a problem for the Republicans.