Lorenzo De Sio Party systems across the Western world appear increasingly challenged. After the 1990s and 2000s saw the prevalence of a two-bloc (or two-party) competition by mainstream parties with relatively similar, moderate policies, recent years have seen an unprecedented emergence of successful challenger parties (and leaders), with examples both on the right-wing (e.g. Donald Trump, the UKIP, the Front National) and on the left wing (e.g. Bernie Sanders, SYRIZA, Podemos, Jeremy Corbyn and Benoît Hamon). Such new, challenger parties and leaders share instead a conflictual emphasis on a relatively small set of controversial policy issues that have proved electorally...