A candidate like Donald Trump should be impossible. A loud, unscripted, hard-edged reality show-style candidate with exceedingly flexible positions on many hot-button issues would be laughed out of contention for the Republican nomination in other years. A man whose serial gaffes and willingness to stick his thumb in the eye of the gatekeepers of good taste would be cooked before he stepped onto the debate stage. An utterly inexperienced politician, who describes our rights and privileges as particular to us as Americans rather than universal moral mandates, would be rejected by both parties at any other time in the modern...