So, Libby is a convicted felon, for what? For having a different memory of two conversations with reporters five years after the fact. This was a travesty, and Bush's unwillingness to set it right with a full pardon shows his weakness quite clearly.
Basically for claiming, in the context of an investigation about who know Mrs. Wilson worked at the CIA, he was damn sure he never contacted the CIA about whether or not Mrs. Wilson worked at the CIA.
GWB believed in the law. Libby doing time would have been the travesty, and Bush prevented that while still respecting the court system. Bush did the same with all his pardons and commutations. Weakness had nothing to do with it.
It was up to Libby to clear his name, something he decided not to do.