Anybody watching American politics closely, or even not so closely, can see some parallels between the Brexit campaign and Donald Trump’s campaign. Both rely on populist sentiments to appeal to white voters, many of whom are in bad economic shape. Both are a reaction to an increasingly diverse country and interdependent world, and both implicitly yearn for a whiter, more Christian time. Similarities between Mr. Johnson and Mr. Trump, are also hard to miss, but easy to overstate. Significantly, Mr. Johnson, unlike the GOP nominee, has years of experience in government, has not demonstrated a principled ignorance on policy questions and is a public intellectual who has written numerous books and articles.