ROME—Last October, Beppe Grillo headlined a protest by the 5 Star Movement, the populist political party he founded. Standing outside the Pantheon he denounced a new electoral law that will limit direct voting for parliamentary candidates and help protect incumbents in national elections on Sunday.
Mr. Grillo, who became famous as a comedian, brandished a white blindfold. “We are protesting blindfolded because this is how they want us—unable to see,” the 69-year-old told a cheering crowd. “They only pass rules that protect...