Josh Marshall, as usual, nails it:
Setting aside whether Scooter Libby should spend 0 days in jail for what most people spend from 1 to 3 years in jail, the key here is that it’s inappropriate for the president to pardon or commute a sentence in a case in which he (i.e., the president) is a party to the same underlying crime. Because it amounts to obstruction of justice.
Is that really so hard to understand? Is there anything he can say to counter it?