ROME — Just over a month ago, Prime Minister Mario Draghi of Italy boarded an overnight train with the leaders of France and Germany bound for Kyiv. During the 10-hour trip, they joked about how the French president had the nicest accommodations. But, more important, they asserted their resolute support for Ukraine in the face of Russian aggression. The pictures of the men tucked in a cabin around a wooden conference table evoked a clubby style of crisis management reminiscent of World War II.

The mere fact that Mr. Draghi had a seat at that table reflected how, by the force of his stature and credibility, he had made his country — one saddled by debt and persistent political instability — an equal partner with Europe’s most important powers. Critical to that success was not only his economic bona fides as the former president of the European Central Bank but also his unflinching recognition that Russia’s war presented as an existential challenge to Europe and its values.

All of that has now been thrown into jeopardy since a multi-flanked populist rebellion, motivated by an opportunistic power grab, stunningly torpedoed Mr. Draghi’s government this week. Snap elections have been called for September, with polls showing that an alliance dominated by hard-right nationalists and populists is heavily favored to run Italy come the fall.

Mr. Draghi’s downfall already amounts to the toppling of the establishment that populist forces across Europe dream of. It has now raised concerns, far transcending Italy, of just how much resilience the movements retain on the continent, and of what damage an Italian government more sympathetic to Russia and less committed to the European Union could do to the cohesion of the West as it faces perhaps its greatest combination of security and economic challenges since the Cold War.

“Draghi’s departure is a real problem for Europe, a tough blow,” said Gianfranco Pasquino, professor emeritus of political science at Bologna University. “Draghi had a clear position against the Russian aggression in Ukraine. Europe will lose in compactness because the next prime minister will almost certainly be less convinced that the responsibility for the war lies with Russia.”

If there was any question of where the sympathies of European leaders lie in Italy’s power struggle, before his downfall Mr. Draghi received offerings of support from the White House, President Emmanuel Macron of France, Chancellor Olaf Scholz of Germany and others.

Prime Minister Pedro Sanchez of Spain wrote “Europe needs leaders like Mario.” When Mr. Draghi made his last-ditch appeal to Italy’s fractious parties to stick with him on Wednesday, Prime Minister Antonio Costa of Portugal wrote him to thank him for reconsidering his resignation, according to a person close to Mr. Draghi.

But now, with Mr. Macron lamenting the loss of a “Great Italian statesman,” anxiety has spread around the continent about what will come next.

Mr. Draghi’s rebalancing of Italy’s position on Russia is all the more remarkable considering where it started. Italy has among Western Europe’s strongest bonds with Russia. During the Cold War, it was the home of the largest Communist Party in the West, and Italy depended on Russia for more than 40 percent of its gas.

Mr. Draghi made it his mission to break that pattern. He leveraged his strong relationship with the U.S. treasury secretary, Janet Yellen, to spearhead the sanctions on the Russian Central Bank.

By the example of his public speeches, he pressured his allies, including Mr. Macron, to agree that Ukraine should eventually be a member of the European Union.

In the days before the fatal vote in the Senate that brought down his government, Mr. Draghi visited Algeria to announce a gas deal by which that country will supplant Russia as Italy’s biggest gas supplier.

Those achievements are now at risk after what started last week as a rebellion within his coalition by the Five Star Movement, an ailing anti-establishment party, ended in a grab for power by conservatives, hard-right populists and nationalists who sensed a clear electoral opportunity, and went for the kill.

They abandoned Mr. Draghi in a confidence vote. Now, if Italian voters do not punish them for ending a government that was broadly considered the country’s most capable and competent in years, they may come out on top in elections.

The maneuvering by the alliance seemed far from spontaneous.

Ahead of the vote, Matteo Salvini, the leader of the hard-right League party, huddled with former prime minister Silvio Berlusconi over a long sweaty lunch at the mogul’s villa on the Appian Way and discussed what to do.

Giorgia Meloni, the leader of the Brothers of Italy, a party with post-fascist roots who has incessantly called for elections from the opposition, said she spoke with Mr. Berlusconi a few days earlier and that he had invited her to the meeting as well, but that she demurred, saying it was better they meet after the vote. She said she spoke on the phone with Mr. Salvini only after Mr. Draghi’s speech in parliament.

“I didn’t want them to be forced to do what they did,” she said, referring to Mr. Salvini and Mr. Berlusconi, who abandoned Mr. Draghi and collapsed the government. “I knew it would only work if they were sure about leaving that government.”

Each has something to be gained in their alliance. Mr. Salvini, the hard right leader of the League party, not long ago the most popular politician in the country, had seen his standing eroded as part of Mr. Draghi’s government, while Ms. Meloni had gobbled up angry support from the opposition, supplanting him now as Italy’s rising political star. Mr. Berlusconi, nearly a political has-been at age 85, was useful and necessary to both, but also could use their coattails to ride back to power.

Together, polls show, they have the support of more than 45 percent of voters.

That is worrying to many critics of Russia. Mr. Salvini wore shirts with Mr. Putin’s face on them in Moscow’s Red Square and in the European Parliament, his party signed a cooperation deal with Mr. Putin’s Russia United party in 2017.

Ms. Meloni, in what some analysts see as a cunning move to distinguish herself from Mr. Salvini and make herself a more acceptable candidate for prime minister, has emerged as a strong supporter of Ukraine.

Mr. Berlusconi used to host Mr. Putin’s daughters at his Sardinian villa and was long Mr. Putin’s closest ally in Western Europe. But now, some of Mr. Berlusconi’s longtime backers say, he has forgotten his European values and crossed the Rubicon to the nationalist and Putin-enabling side.

Renato Brunetta, Italy’s Minister for Public Administration, and a long time member of former Prime Minister Silvio Berlusconi’s Forza Italia, quit the party after it joined with the populist League party in withdrawing support from Mr. Draghi and destroying the government.

He said he left because Mr. Berlusconi’s decision to abandon the government was irresponsible and antithetical to the values of the party over the last 30 years. Asked whether he believed Mr. Berlusconi, sometimes shaky, was actually lucid enough to make the decision, he said “it would be even more grave” if he was.

Italy, long a laboratory for European politics, has also been the incubator for the continent’s populism and transformation of hard-right movements into mainstream forces.

When Mr. Berlusconi entered politics, largely to protect his business interests in the 1990s, he cast himself as a pro-business, and moderate, conservative. But in order to cobble together a winning coalition, he had brought in the League and a post-fascist party that would become Ms. Meloni’s.

Now the situation has inverted. Ms. Meloni and Mr. Salvini need Mr. Berlusconi’s small electoral support in order to win elections and form a government. They are in charge.

“It is a coalition of the right, because it is not center-right anymore,” said Mr. Brunetta. “It’s a right-right coalition with sovereigntist tendencies, extremist and Putin-phile.”

Supporters of Mr. Draghi take some solace in the fact that he will stick around in a limited caretaker capacity until the next government is seated, with control over issues related to the pandemic, international affairs — including Ukraine policy — and the billions of euros in recovery funds from Europe. That money is delivered in tranches, and strict requirements need to be met before the funds are released.

Supporters of Mr. Draghi acknowledged that major new overhauls on major problems such as pensions were now off the table, but they argued that the recovery funds were more or less safe because no government, not even a hard-right populist one, would walk away from all that money, and so would follow through on Mr. Draghi’s vision for modernization funded by those euros.

But if the last week has shown anything, it is that political calculations sometimes outweigh the national interest.

The government’s achievements are already “at risk” over the next months of Mr. Draghi’s limited powers, said Mr. Brunetta, but if the nationalist front won, he said, “obviously it will be even worse.”

Mr. Brunetta said Mr. Draghi arrived on the political scene in the first place because there was a “crisis of the traditional parties” in Italy. He said that the 17 months in government, and the support it garnered in the public, showed that there was “a Draghian constituency,” which wanted moderate, pragmatic and value-based governance.

The problem, he said, was there were “no political parties, or especially a coalition, to represent them” and he hoped one could be born before the election but “there was little time.”

And in the meantime, he said, some things were for sure. Italy had lost influence in Europe and the continent would suffer, too, for the loss of Mr. Draghi.

“Europe,” he said, “is weakened.”

Gaia Pianigiani contributed reporting.