We are witnessing the beginning of act two in the drama of Italian populism, and it is a showdown between the protagonists who made phase one happen. Since the election of 2018, Matteo Salvini’s League has grown stronger, and it has had enough of its coalition partner, the Five Star Movement. It now feels it can claim sole leadership of the country, with Salvini as prime minister.

It’s a development that Steve Bannon, the theoretician of the US populist wave that elected Trump in 2016, foresaw. The day after the coalition was formed, Bannon said of Salvini and the Five Star leader, Luigi Di Maio: “They will govern together, but Salvini is the real leader, because Di Maio resembles [Emmanuel] Macron.” This was always a tactical alliance, because in the end populism is based on there being only one leader.

What’s coming will be aggressive and confrontational. Act two of Italian populism will put up a tough fight

Act one of this new Italian political phenomenon – last year’s game-changing general election – testified to a solid populist majority among the electorate. But the coalition that resulted highlighted the deep differences between the allies. The European elections of 26 May, in which the League won twice as many seats in the European parliament as the Five Star Movement, signalled to Salvini that the time was finally right to trigger act two. The League’s motion of no confidence in the current prime minister, the lawyer Giuseppe Conte, is designed to test whether the project can be pulled off or not. On Tuesday, in a moment of truth, Conte will face Italian MPs over the crisis.

This is about the re-making of Italian populism in the image of the aggressive nationalism of the League. The Five Star Movement, which has been more ambiguous in its political positioning, is increasingly seen as a collection of losers.

What we are seeing is essentially a revolt of the Italian middle classes. It started out as a protest against inequality, migrants and corruption; it has grown in strength by generating conflicts and new enemies, and it craves a strong leader rather than a complicated, amorphous alliance.

The nationalism of the League involves closing ports to migrants; planning to impose fines of up to €1m on anyone assisting a refugee at sea; voting in Strasbourg against the new president of the European commission and aiming to make the next budget a platform for openly challenging Europe over its fiscal rules. With Salvini at the helm, it all plays out in a public performance featuring crucifixes, beach orations, the vocabulary of football ultras and a tribal exaltation of ethnic-nationalist identity. The hostility to migrants and the duel with Europe are the two pillars around which Salvini garners votes, making mincemeat of the Five Star Movement, which is banking on a policy of offering a basic income to “defeat poverty”. That was too vague an objective to ever be credible.

Now Salvini is getting ready to pounce on his former allies. In order to see him off, the Five Star Movement would have had to transform itself into a credible force for government and a guarantor of stability. It would have had to move on from protest to the art of governing.

The reason it wasn’t able to is because it was wedded to an anti-growth ideology, which led it to commit a series of errors. It was a mistake to oppose Rome’s nomination for the 2024 Olympics and Turin’s for the 2026 Winter Games. It was a mistake to oppose a high-speed train link between France and Italy, a new motorway in the north of Italy, and a project to drill for oil in territorial waters off the coast. The Five Star Movement has given the impression that it opposes the modernisation of the country.

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As a result it lost the leadership of the protest movement: first it was wiped out at the regional elections, then it was humiliated at the European elections. Now, with a possible no-confidence vote against Conte, it may lose its prime minister of choice. In this new phase of Italian populism, the nationalists will be in charge, possibly as the result of a deal between Salvini and Giorgia Meloni’s far-right Brothers of Italy party. The country will move even closer to emulating Poland and Hungary. The Five Star Movement will be left with the desperate choice of going under or allying itself with the traditional mainstream parties in an attempt to stop its ex-comrades-in-arms.

What’s coming will be aggressive and confrontational. Act two of Italian populism, if Salvini is in charge, will put up a tough fight against anyone trying to get in its way. His political adversaries will have to choose between forming a coalition government in the current parliament, bringing together all the anti-Salvini forces, or a head-on challenge at the polls. Either way, this clash will become a kind of referendum on national identity and the relationship with Europe. The next phase of political struggle in Italy is destined to be a duel between extremes.

• Maurizio Molinari is the editor-in-chief of La Stampa