More Scooter speculation

I think I have an answer to the question TPM Muckraker asks here:

But here's what we don't get yet about the defense's theory of the case, as TPM Reader LG puts it: "while it may be true that the [White House] was trying to hang Libby out to protect Rove, this in no way absolves Libby from charges of perjury and obstruction of justice. How is that a defense? Seems like just a smokescreen to me."

This puzzled me too for awhile, but I think I have the answer. Fitzgerald is planning to call a number of government witnesses from the White House who will testify that they either told Libby about Plame before Libby talked to Tim Russert (from whom he claims he got the information about Plame) or that he told them about Plame before he talked to Russert. This may be an attempt to impeach those witnesses by suggesting they are in on the plot to pin the blame on Libby in order to protect Rove.

It doesn't seem to me that it has much punch from a legal point of view (obviously he's not trying to charge them with perjury) but it may have an influence on the way the jurers hear the testimony from those witnesses.