With Virginia Raggi tipped to become Rome's first female mayor after a run-off vote this weekend, the spotlight has turned to M5S's performance in smaller cities where it already holds power.
Viriginia Raggi. Photo: Filippo Monteforte/AFP
It is a record that is mixed in Parma (population: 200,000) and Livorno (160,000), both of which have had mayors elected on an M5S slate since the last set of local polls in 2014.
"The impression is that the actions of these mayors have led to disappointment. They raised hopes so highly that they were impossible to be fulfill and inevitably a certain disillusionment set in afterwards," said
Lorenzo De Sio, a professor of political sociology at the Luiss university in Rome.
Founded by comedian Beppe Grillo, Five Star has established itself as the primary opposition force in Italian politics against a backdrop of deep divisions on the right between centrist allies of fading figurehead Silvio Berlusconi and a far right tendency led by the Northern League.
Grillo's movement insists it belongs to neither left nor right, basing its appeal instead on a call for voters to throw out an established political class it depicts as chronically corrupt and incapable of change.
That is why the problems encountered by mayors, Federico Pizzarotti, in Parma, and Filippo Nogarin, in Livorno, have presented M5S with a knotty presentational problem and highlighted the scale of the challenge involved in trying to be a "party unlike the others".
"The movement has a major problem, it does not have a stock of experienced people and the two mayors had problems finding officials to appoint to different sections of their respective administrations," said De Sio.
M5S activists have split over the different treatment the two mayors have received from the party in reaction to relatively minor legal woes they have encountered.
Nogarin is seen as having been let off lightly after prosecutors began looking at the recruitment of new staff at the city's near-bankrupt refuse collection company.
Pizzarotti, who is more critical of the leadership, has been suspended from the party pending the outcome of a probe into his decision not to follow an advisory committee's recommendation over the appointment of a new director of the local opera.
In Parma, M5S displaced the centre-right, which had governed the city for most of the previous 20 years, while in Livorno, a gritty port that was the birthplace of the Italian Communist Party, the left had been in control continuously since the end of World War II.
"We inherited a disastrous situation due to 20 years of awful administration of the town and we started by making a study of the extent of the damage," Nogarin said in an interview with AFP in Livorno's town hall.
High stakes in Rome
"So, for example, companies in which the town is the main or only shareholder had accumulated debts of more than €200 million."
Prime Minister Matteo Renzi's Democratic Party (PD) accepts some of the blame for the situation but insists M5S has made things worse.
"That the PD lost the town was partly its own fault - after so many years in power its appeal had waned," admitted Andrea Romano, a PD parliamentary deputy for the city.
But he adds: "M5S represents a cocktail of administrative incompetence and populist propaganda. They took over a town that had been hit hard by the economic crisis and its debt but all they have done is make things worse and given us the highest taxes in Tuscany."
On the streets, opinions are mixed. "The new mayor has not made anything better for me," said 78-year-old pensioner Giancarlo. "Livorno is half-dead, there is nothing left here. It is worse than before."
But Luciano Marchioni, 57, says M5S has done okay. "In my opinion, the situation has clearly improved. The only thing I'd say is that I had expected something more radical, more investments in the town."
In Rome, all the signs are that voters are set to elect Raggi as their first female mayor. But the stakes will be much higher, the price of failure far greater.