Italy's ruling Democratic Party (PD) is as divided as France's Socialist Party, and the Social Democrats (SPD) in Germany. Since 2013, the party has been split between so-called reformists-realists, represented by former Prime Minister Matteo Renzi, and a minority that advocated for a more traditional version of social democracy, complete with a strong agenda for economic redistribution - a split that has now become common in Europe.

When Renzi was defeated in the December 2016 referendum for k...