The electoral system and electoral geography -why the Rosato law appeared to be proportional while it is not

The 2018 elections confirmed the tri-polar format of the party system, with three opposing aggregations, each of which has a majority (or at least enjoys considerably more support) in a specific area of the country. The paper shows that, in a way, the highly unequal geographical distribution of the vote is revealing of the main social factors underlying the choices of voters. In another respect, it masks the potential disproportionality of the electoral system. The paper also shows that uncertainty about the possible evolution of alliances between parties, the risk that early elections could again produce a hung Parliament, and the high level of mobility of the electorate, make it probable that the electoral law will at some time in the near future, once again be subject to revisions driven by the short-term interests of the political actors involved. In this regard, the paper discusses the nature of the so called ‘Rosatellum’ as a majoritarian or proportional mixed-member electoral system. It proposes an estimate of the SMD candidates’ electoral performances and of the minimum support for the most voted coalition and the minimum level of territorial uniformity of the vote required for the Rosato law to produce a parliamentary majority. Finally, it discusses the possible adaptations of the law that could facilitate such a result.