few indicators that Mr. Trump had a good chance of beating Ms. Clinton were his enormous leads on Facebook and Twitter throughout the 2016 campaign. Applying similar metrics around the world yields startling results. Take Britain, for example. The Leave campaign's victory in the 2016 referendum on Britain's membership in the European Union owed a great deal to its pioneering use of Facebook advertising. Yet the principal political beneficiary of Brexit – the woman who became prime minister shortly after the referendum, Theresa May – is a social-media loser, with little more than half a million Facebook followers and even less on Twitter. By comparison, the Labour Leader Jeremy Corbyn – a grizzled populist of the left in the style of Bernie Sanders – has 1.3 million followerswhose political elite has been battered by corruption scandals that led to the impeachment of the Workers' Party President Dilma Rouseff and probably disqualify her predecessor, Luiz Lula da Silva, from running this year. But who cares? Lula has three million Facebook followers and just 189,000 Twitter followers. Far ahead of him on social media is Luciano Huck, the entrepreneur and television star, host of the hugely popular Saturday night TV show Caldeirao do Huck. With 17 million Facebook followers and nearly 13 million on Twitter, Mr. Huck is in a league of his own in Brazilian politics.

A Huck candidacy would be the Brazilian equivalent of Oprah Winfrey (FB 11.6m, TW 41.4m) running for president in 2020. He is not a populist; he's just popular. In second place,