None of which changes the fact that she could have been charged with other crimes, or another round of contempt, if not pardoned by Clinton.

Does that mean, per se, that Clinton was trying to insulate himself from further criminal investigation? Of course not.

At the same time, however, there little evidence that Bush's commuting Libby's sentence was an attempt to insulate himself from further criminal investigation.

Furthermore, to continue your comparison of McDougall and Libby, since McDougall was pardoned, there was no chance she would be charged again or serve more time. Accordingly, there was no threat against her and, as a result, no threat that could pressure her to testify against Clinton.

In contrast, Libby still faces a quarter of a million dollar fine and years of probation. When a person is on probation, they are required by court order to obey certain terms and conditions including, typically, cooperation with probation officers and government officials investigating crimes. As a result, if Libby fails to cooperate in any investigation of Bush he can be found in violation of his probation and resentenced.

And, do you really think that, if Libby violates his probation, the Special Prosecutor Fitzgerald wouldn't act to have him sent to jail?

Accordingly, if anything, Bush's actions increase the chance of Libby having to testify (assuming that he has something to testify to).