Bush's commutation is nothing like those outrageous acts of clemency. It is perfectly in the mainstream of pardons throughout the past 20 years in cases that are considered politicized prosecutions by the aggrieved administrations. The Founders created the pardon power to grant relief from a justice system that might, in the words of Alexander Hamilton, be "too sanguinary and cruel." It doesn't serve that function so much anymore, but has turned out to be a safety valve in an era when each party criminalizes political disputes when it suits its purposes.
This creates a perpetual argument over whose perjury is worse. Liberals say that Libby's perjury is more serious than Clinton's because Libby lied about the war and Clinton lied only about sex. Actually, Libby's case wasn't about the war, but about whether or not he had misremembered when and from whom he first had heard that Joe Wilson's wife, Valerie Plame, worked at the CIA. There also is an ambiguity to Libby's case, with its complex assortment of conflicting memories, that didn't exist in that of Bill Clinton, who admitted to testifying falsely under oath.
Regardless, except for the most blatant crimes, the political arena is the best forum for politically controversial charges of wrongdoing. Rather than commuting Libby's sentence on grounds that it was excessive, Bush should have pardoned him altogether on grounds that the case had become a way to make one man pay for the alleged sins of the administration regarding the war. Our system of government provides a straightforward method to punish an administration without resorting to special prosecutors and criminal charges, which is to vote against the president or his party.
Just wait: The same people hyperventilating about Libby now will have exactly the opposite attitude about the criminalization of politics when a Democrat is back in the White House. Then, they will grow fond of Article II, Section 2 all over again.