Leave aside for a moment whether it was wise for President Obama to order our military to intervene in Libya's civil war, siding with rebels we know little about against a dictator who has sponsored terrorism against us. A more fundamental question comes first: Did Obama have constitutional authority to do it? President Washington's actions counsel otherwise. In responding to Indian raiders, Washington repeatedly declined to order offensive -- as opposed to defensive -- military action because Congress had not approved it, as he believed the Constitution required. In 1792, William Blount, governor of the territory that became Tennessee, wrote...