N COMMUTING I. Lewis Libby's prison sentence yesterday, President Bush took the advice of, among others, William Otis, a former federal prosecutor who wrote on the opposite page last month that Mr. Libby should neither be pardoned nor sent to prison. We agree that a pardon would have been inappropriate and that the prison sentence of 30 months was excessive. But reducing the sentence to no prison time at all, as Mr. Bush did -- to probation and a large fine -- is not defensible. Mr. Libby was convicted in March on charges of perjury, making false statements and obstruction...