The most potent moment of the Democratic convention last week was when Khizr Khan, father of an Army captain killed in Iraq in 2004, challenged Donald Trump's proposal to ban Muslims from entering the United States. "You have sacrificed nothing and no one," Khan said to Trump, holding aloft a copy of the Constitution that he suggested Trump read. Trump's immediate response was to criticize Khan and his wife, earning a number of rebukes from veterans and members of his own party. "There are certain sacrosanct subjects that no amount of wordsmithing can repair once crossed," said a statement from...