It is entirely possible that Cooper is the first to see what horrors could come out of the discovery process and a trial. I believe the game plan was for Libby to plead the charges down so all of this would go away.
Looks like maybe the prosecutor and Libby played showdown and Matt Cooper blinked.
This whole thing was to win the left the WH a year ago - it imploded, thanks to Judy Miller, and now the discovery process hopefully will uncover the Hillary-inspired conspiracy that it really is, with a few nations thrown in who should be charged with attempting to influence a US presidential election.