For years I’ve been arguing that Donald Trump is a world-class persuader. So why is his job-approval rating so low? The short answer is that the old rules about presidential approval no longer apply.

Do you remember a few decades ago when one of the main complaints about politics was that Democrats and Republicans were not so different? Not anymore. The news industry has found that polarization is a strong business model. The first group of pundits claim many times a day that Republicans are right about nearly everything and...