Why are populists so popular?

They claim to speak for the people and fight the elite. From Donald Trump in the United States to the National Front in France, Nigel Farage and the UK Independence Party, Geert Wilders and the Dutch or indeed Austrian Freedom Parties... populists' appeal is growing. So is it power to the people or a degraded form of democracy? We ask Jan-Werner Müller, a professor of politics at Princeton University and the author of a new book entitled "What is populism?"