David Frum begins “Trumpocracy: The Corruption of the American Republic” with a quotation from Montesquieu, the French philosopher who had a profound impact on America’s Founding Fathers. A free society, Montesquieu wrote, must guard not only against the crimes of leaders, but against “negligence, mistakes, a certain slackness in the love of the homeland, dangerous examples, the seeds of corruption, that which does not run counter to the laws but eludes them, that which does not destroy them but weakens them.”