Whenever Donald Trump and his followers are confronted with his evidence of his abysmally terrible polling numbers on personal favorability and versus Hillary Clinton, they typically respond with a pair of deflections. First, they say that Trump "hasn't even started" attacking Hillary yet. Setting aside the fact that Trump has taken many hard jabs at Mrs. Clinton over a span of months, this line of thinking requires a logical leap: That once he does train virtually all of his fire on her, it will both hurt her and help him. American voters have been subjected to endlessTrump coverage since last spring, over...