Far-right League leader Matteo Salvini won a crushing victory in the Italian region of Umbria, results on Monday showed.
Parties in the coalition, the anti-establishment 5-Star Movement and centre-left Democratic Party (PD), stood together on a joint ticket for the first time in the Umbrian election but won only 37.6% of the vote.
The centre-right candidate supported by Salvini won 57.5% of the vote.
It was the first time in half a century that the centre-left had lost control of Umbria.
Is Italy's ruling coalition at risk after Salvini's triumph in the central Italian region? Euronews answers.
According to Salvini, the results in Umbria hold national significance.
"The results we have seen in Umbria, we are seeing all over the country. This is not a government that represents the Italian people," Salvini told Radio 24.
"I don't think it can go on for much longer," he added, repeating his demand for early parliamentary elections.
But Prime Minister Giuseppe Conte, who is close to 5-Star, said the Umbrian rout should have no bearing on his government.
"We are here to govern with courage and determination. A regional vote cannot in anyway influence our actions," Conte told reporters. "If we have no courage, determination or foresight it would be better for us to go home."
Speaking to Euronews, expert Teresa Coratella based at the Rome Office of the European Council on Foreign Relations (ECFR) told Euronews that while the election was a "great success for the League," the Umbrian population only made up 2% of Italy's population.
"Of course, there will be an impact but this election doesn't reflect the political situation in our Parliament," Coratella said.
With 216 seats, the 5-star movement remains the dominant political force in Italy's Chamber of Deputies, followed by the League (124 seats).
In a political miscalculation, Salvini walked out of a coalition with 5-Star in August, expecting his move to trigger a national ballot that polls predicted he would easily win.
Instead, 5-Star hooked up with the PD, hoping they could erode Salvini's support as he languished in opposition.
But Sunday's vote showed the League, pushing an anti-migrant, tax-cutting agenda, is by far Italy's most popular party.
The League won 37% of the vote, while its nationalist ally Brothers of Italy took 10.4%.
Former prime minister Silvio Berlusconi's Forza Italia, for years the strongest party within the centre-right bloc, limped home with a meagre 5.5%.
The PD clinched 22.3%, slightly down on what it won in Umbria in European parliamentary elections in May.
5-Star now 'weaker link' in coalition
The poor showing of the 5-Star movement is one of the major takeaways from the election, Coratella told Euronews.
The movement slumped to 7.4% in Umbria -- half of what it chalked up in the EU ballot
"The major result is that 5-Star is now the weaker link in the coalition," Coratella said.
5-Star blamed the results on the decision to present a joint candidate with the PD -- its traditional political foe before their surprise alliance in August.
"The experiment did not work," the party said in a statement. "This shows that we can only really represent a third way by looking beyond the two opposite poles."
The PD took comfort from the fact that its own vote did not collapse in Umbria, but said recent cabinet infighting over the 2020 budget had hurt the image of the ruling coalition.
Major regional vote in January
The key test for the ruling coalition will be on January 26, when Emilia Romagna votes in local elections, Coratella said.
The northern region has more than four times the population of Umbria and is the historic heartland of Italy's left.
If the current coalition also fails in Emilia-Romagna, then it will be seriously at risk, Coratella told Euronews.
"We are coming," Salvini wrote on Twitter on Monday, announcing his first big campaign rally in Emilia for Nov. 14.
Italian governments have collapsed in the past on the back of weak showings in regional ballots and defeat for the centre-left in Emilia Romagna would be a political earthquake that would put enormous strain on the 5-Star/PD coalition.
Some newspapers have speculated that the outgoing European Central Bank President Mario Draghi might be asked to try to form a government of technocrats should the current administration fall.
Salvini dismissed such a prospect as "disrespectful" for Italians. "If this government falls, the only way forward would be new elections," he said.