ITALY’s governmental crisis was already the longest since the foundation of the republic after the second world war. It has now become a constitutional crisis, with implications for the entire European Union. As the leader of its biggest party called for President Sergio Mattarella to be impeached for refusing to install western Europe’s first all-populist government, Italy appeared to be heading for fresh elections at which anti-establishment parties were expected to increase their parliamentary majority.

On the morning of May 28th, Mr Mattarella summoned Carlo Cottarelli (pictured), an economist and former IMF official with no experience of politics, to the presidential palace and asked him to form an interim cabinet of non-party technocrats to steer the country back to the polls. Mr Cottarelli had been preceded to the palace on the night of May 27th by Giuseppe Conte, the candidate for prime minister of the anti-establishment Five Star Movement (M5S) and the hard-right Northern League. Together, the two populist parties won half the votes in the election on March 4th. Mr Conte left to announce that the president had vetoed the government that he and his sponsors—Luigi Di Maio, the leader of the M5S, and Matteo Salvini, the head of the League—had proposed. He said he had called off his attempt to form a government.

As Mr Mattarella later explained, it was just one minister in their intended cabinet he had balked at appointing: Paolo Savona, an 81-year-old economist proposed for the job of finance minister. Mr Savona is a dogged critic of the euro and the author of a plan for extracting Italy from the single currency area. The president said he could not agree to “a minister [who is a] supporter of leaving the euro”. Swearing him in might indeed have panicked capital markets, which are already agitated by the prospect of a populist partnership running the euro-zone’s third-largest economy. The M5S and the League favour big spending increases and tax cuts aimed at reviving Italy’s sluggish economy, despite its public debt (132% of GDP at the end of 2017). The president said he had a duty to safeguard Italians’ investments.

Markets appeared confused by Mr Mattarella’s intervention. The difference in the yield on Italian and German benchmark government bonds, an indicator of investors’ concern about Italy, initially shrank from over 200 basis points to 190 on the morning of May 28th, but then returned to its earlier level. The Milan bourse and the euro quickly gave up early gains.

Well might they dither. The probable beneficiary of fresh elections is the League, the more Eurosceptic of the two prospective coalition partners, whose poll ratings have climbed steadily since March. A return to the polls could also benefit the M5S, which advocates a mixture of left- and right-wing policies, and would be well placed to lure yet more progressive voters away from the deeply divided Democratic Party (PD).

The other question still to be answered about the president’s dramatic move is whether it was legitimate. The 1948 constitution is less than clear-cut: it says the president appoints the prime minister and “on his proposal, the ministers”. Mr Mattarella blocked the choice of two parties that together command majorities in both houses of parliament, and on the grounds that they wanted a minister suspected of seeking to remove Italy from the euro. That would seem to mean that Italy can never leave the single currency, and that when push comes to shove, the bond market has more clout than the ballot box. But Mr Matterella insisted, at the very least, that there be a proper national debate before any moves in that direction.

Mr Di Maio, whose party won more votes than any other at the election, accused Mr Mattarella of a premeditated operation, intended to stymie the formation of a coalition with the League. Clearly hinting at a plot between the president and the guardians of euro-zone orthodoxy, Mr Salvini said Mr Mattarella had “represented the interests of other countries; not of the Italians.”

His is not the only conspiratorial interpretation being discussed in Rome. Another theory has it that the M5S and the League had deliberately refused to back down over Mr Savona in order to force a snap election, hoping thereby to strengthen their position.

Mr Salvini said: “We want a date for the elections. Otherwise we truly shall go to Rome.” He must have known his words would be taken by many Italians as an allusion to an earlier constitutional crisis, in 1922, which Benito Mussolini’s Fascists exploited to seize power by means of a “march on Rome”. Such talk at such a sensitive moment is at best wildly irresponsible. At worst, it is deliberately subversive.