For the past half decade, Europe has acted as a preview of coming attractions in American politics. The reaction to the confluence of immigration and terrorism on the continent foreshadowed the direction the Republican Party would take under Donald Trump. The surprise victory of “Leave” in the Brexit referendum hinted at Trump’s unexpected elevation to the presidency. The terrible images from coronavirus-stricken Italy last March offered a glimpse into New York City’s future. This week, when Italian authorities reimposed curfews, restrictions on business, and bans on communal gatherings, violent protests broke out in Turin, Milan, and Naples. Consider it a taste of the next populist revolt.