Mr. Berlusconi was able to govern Italy for as long as he did mostly thanks to the incompetence of his opposition. It was so rabidly obsessed with his personality that any substantive political debate disappeared; it focused only on personal attacks, the effect of which was to increase Mr. BerlusconiĀ’s popularity. His secret was an ability to set off a Pavlovian reaction among his leftist opponents, which engendered instantaneous sympathy in most moderate voters. Mr. Trump is no different.

…The Italian experience provides a blueprint for how to defeat Mr. Trump. Only two men in Italy have won an electoral competition against Mr. Berlusconi: Romano Prodi and the current prime minister, Matteo Renzi (albeit only in a 2014 European election). Both of them treated Mr. Berlusconi as an ordinary opponent. They focused on the issues, not on his character. In different ways, both of them are seen as outsiders, not as members of what in Italy is defined as the political caste.