His legal staff anticipated all of these issues. It is a very narrow prosecution. As long as it remains narrow, and he defends how narrow it is, Libby's attorneys will have trouble.
The instructions to the jury will not involve anything about the underlying investigations. They will focus strictly on whether or not all statements by Libby to the GJ were accurate. Why the investigation is being conducted will be of no interest to a jury.
The only time that question could have merit is with a judge. If this goes to trial, and entirely different defense will be necessary.
Is there not a distinction between whether his statements to the GJ were "accurate" and whether or not he intentionally mislead the GJ?