IN BARELY seven years, the populist Five Star Movement (M5S), has become Italy’s biggest opposition group. As the country approaches a referendum on December 4th that could lead to the fall of Matteo Renzi’s left-right coalition and a renewed bout of political turmoil, the M5S is just a few percentage points behind Mr Renzi's Democratic Party (PD). At the last election in 2013, the M5S took a quarter of the vote. Since then, Silvio Berlusconi’s Forza Italia party—once the PD’s principal rival—has imploded. Italy’s other main right-wing party, the Northern League, has so far been unable to take its place; its appeal constrained by its regional character and extreme views. Against this background, an M5S government is no longer unthinkable. In June, its candidates for mayor won in Rome and, more surprisingly (and traumatically for the PD) in Turin, a left-wing stronghold. What exactly is the M5S, and what does it stand for?

Neither of the two men who founded the movement in 2009 was a politician at the time. One was Beppe Grillo, a comedian in the mould of Michael Moore or Russell Brand. Mr Grillo has lent the M5S visibility and celebrity charisma. But it was his co-founder, Gianroberto Casaleggio, an IT executive, who gave it its distinctive character. Mr Grillo wrote that he first took the shaggy-haired internet buff to be a lunatic, but soon concluded he was a visionary. Mr Casaleggio persuaded the comedian—banished from television because of his attacks on the powerful—to start a blog. He then encouraged devotees of the blog to use the Meetup platform to form the local cells that laid the foundations for the M5S.

At the core of the movement’s philosophy is the view that it is not a party, but an organisation set up to get rid of parties, which many in Italy view as sources of patronage and graft. This is one of the things that distinguishes the M5S from other disruptive political groups such as Podemos or UKIP. The latter use the internet to rally support. The M5S sees it as the very reason for its existence: a medium remorselessly eliminating mediation of all kinds that will eventually destroy parties and make possible a form of direct democracy if the people control the government through constant voting over the web. This idealistic, almost Messianic, vision explains some of the Movement’s other distinguishing traits: its refusal to do deals with the pre-existing parties, its cult-like nature (dissidents are regularly purged in online ballots) and its insistence that it is neither of left nor right (since it aims to embrace the entire electorate).

Though most of the M5S’s leadership came from the left, it has picked up large numbers of votes on the right. Facing in both directions at once, it is a fearsome opponent, especially in two-round elections of the sort introduced by Italy’s new electoral law: having eliminated, say, Forza Italia in the first round, the movement can then scoop up many of the eliminated party’s voters in the second. But that very advantage makes it vulnerable: its left- and right-leaning members are increasingly clashing over policy, and forming informal factions within the movement. The other big challenge it faces is to show its elected officer-holders can overcome their inexperience to govern effectively. The new M5S mayor of Rome has made a disastrous start. If the movement cannot run a city, voters may conclude, it should not be given charge of a country.