Dick Cheney told FBI investigators he wasn't happy when Scott McClelllan, then the White House press secretary, publicly told reporters that Karl Rove wasn't the source of the Plame leak.
From the just-released documents
The Vice President was not happy about it, as it appeared that the White House press office was putting down markers for some individuals and not for others. Specifically, Vice President Cheney believed that fairness dictated that similar disqualifying statements should be made to the media on behalf of Libby and Elliot Abrams of the NSC, both of whom were the speculative targets of leak allegations by the media that week.
In other words, Cheney wanted Libby and Abrams exonerated in addition to Rove.
Of course, we now know that both Rove and Libby did
leak Plame's name to reporters, though not to Novak.