Rarely can Presidents improve their legacy in an Administration's twilight days. But President Bush now has that opportunity, by undoing a measure of the injustice inflicted on I. Lewis "Scooter" Libby.

As the former chief of staff to Vice President Dick Cheney who suffered in a fiasco made worse by the White House, Mr. Libby deserves a full Presidential pardon. Mr. Bush commuted Mr. Libby's sentence in 2007, an action that kept him out of jail. But that doesn't expunge his conviction for perjury and obstruction of justice....