The President has authority to commute a sentence, but not to obstruct justice

The President has the authority to commute a sentence - but that is a separate issue from the possibility of obstructing justice. Commuting Scooter Libby's sentence removes the pressure on him to testify about whatever it is he lied about to Patrick Fitzgerald. Evidence indicates that those lies were intended to cover up Cheney's actions, and potentially Bush's own actions, in trying to obscure the facts behind their drumbeat for war. If there was any cooperation or communication behind the commuting of the sentence, or if Bush commuted the sentence with the expectation that it would help prevent his own and/or Cheney's misdeeds from coming to light, that is an entirely separate issue from the mere authority to commute a sentence. Whether this was the case demands further investigation.