MELENDUGNO, Italy — When Alfredo Fasiello voted for the Five Star Movement this year, he believed the party would join his battle against a 545-mile, $5.2 billion pipeline to bring gas from the Caspian Sea to Italy, landing near the small beach club his family owns in San Foca, on the heel of Italy.
Now that Five Star is a partner in government and its political leader, Luigi Di Maio, is the minister for economic development, the party’s internal disagreements, apparent reservations and wavering on opposing the pipeline have left Mr. Fasiello and other southerners who helped vault the party to victory verging on revolt.
“We hoped they would have a trace of the honesty and transparency that they talk so much about. They were here 1,000 times,” Mr. Fasiello, 62, said on a recent summer day.
“If Five Star betrays us, they will never win another vote here,” he added. “They’ll be ashamed to show up on the beaches. It’s not just this area. If they betray us, everyone will know not to trust them.”
Five Star came to power by harnessing Italy’s anger toward politics-as-usual and big business interests, running a nationalist-themed campaign filled with conspiratorial overtones against globalist forces and suspicion of expertise and the elite — whether it came to vaccines, economics or energy.
The Trans Adriatic Pipeline, or TAP, now poses an existential political problem for Five Star. The project has confronted the party, previously untested at a national level, with choices of governing in an interconnected world with real-life consequences.
Italy imports 90 percent of its energy, and the United States and the European Union have long pushed the pipeline as a strategic priority to wean the country off its dependency on Russian oil and gas and to reduce Russian influence in Europe.
While the relationship between the United States and Russia has grown more complicated under President Trump, he still appears to back the pipeline as a competitor to Russia’s Nord Stream 2 pipeline, which he recently tweaked Chancellor Angela Merkel of Germany for supporting.
Sputnik, the Kremlin-aligned news outlet, recently called TAP “Trump’s Tool” in an economic war with Russia.
Both Five Star and its governing partner, the League, are opponents of sanctions against Russia and proponents of closer ties to Russia’s president, Vladimir V. Putin, and neither party has seem moved by a strategic motivation to limit Russia’s sway.
Yet under pressure from the United States, the European Union and international business interests, Five Star is awkwardly walking back its opposition and stalling in the face of billions of euros in penalties and the loss of credibility for future investment.
Matteo Salvini, the leader of the League, recently insisted that the pipeline needed to be finished to lower gas prices and help the country’s impoverished south.
But the pipeline, slated for completion in 2020, has been bitterly opposed by many in Puglia, a region famed for its scenic coastline, turquoise waters and shimmering olive groves, and one that was critical to Five Star’s electoral success.
“No TAP” signs and graffiti cover the walls, dumpsters and boardwalks all around the southern coast. On a recent summer day, Mr. Fasiello took a walk with a fellow activist, Graziano Petrarchi, on the beach and pointed at a family sunbathing and children building a sand fort above the pipeline’s projected route.
“Would you ever bring your child swimming here? With an atomic bomb underneath? It’s a tumor,” he said of the pipeline. “It’s three meters in diameter, and you can drive a car through it.”
The two recalled how Barbara Lezzi, a prominent Five Star politician from the nearby city of Lecce, who is now the government’s minister for the south, built her campaign around her opposition to the pipeline and held flash-mob protests on the beach.
Beppe Grillo, the co-founder of Five Star, marched against the pipeline in 2014, and in April 2017, Alessandro Di Battista, the party’s “Baywatch”-worthy rabble rouser, visited the beach and promised that, once in office, Five Star would block the pipeline “in two weeks.”
That time has long come and gone.
Italy’s president, Sergio Mattarella, flew to Azerbaijan in July to guarantee that Italy would not impede the completion of the pipeline, which would hook up with pipelines in Turkey and run through Greece and Albania to, finally, Italy.
That was enough for Marco Potì, 48, mayor of Melendugno, the tiny town near San Foca. A longtime socialist supporter, he instead voted for Five Star in March with every expectation that the party would live up to its promise to block the pipeline.
“He’s never returned the letter of 97 mayors” who wrote him opposing the project, Mr. Potì said as he reached up and removed Mr. Mattarella’s portrait from the wall the very next day after the president went to Azerbaijan. “But he shakes the hand of a dictator who crushes his people. He disrespected his citizens.”
In July, Mr. Trump pressed Italy’s prime minister, Giuseppe Conte, on the issue during a meeting at the White House. Mr. Conte, who is aligned with Five Star, made Melendugno his first destination upon returning to Italy, where he listened to Mr. Potì’s concerns and promised an “in-depth assessment.” But he also called the project “strategic” for Italy.
Russia analysts say efforts in Bulgaria, Poland and elsewhere to diversify from Russian energy have spawned environmental groups, suspected of operating with Russian backing, that have slowed down or stopped the projects.
Mayor Potì “completely excluded” the accusations of Russian meddling. “These are fables,” he said.
There has been no evidence of Russian interference in the pipeline.
Activists say there is no need. Mr. Fasiello said the “strategic” rationale of the pipeline was a farce because Russia had found a way to sell its gas to Azerbaijan and to get it into the southern pipeline anyway.
“Sputnik and even Putin says that Azerbaijan will get gas from Russia,” Mr. Fasiello said.
International agreements stipulate that for 25 years the initial 10-billion-cubic-meter volume of the pipeline can carry gas only from the Azerbaijani Shah Deniz fields, essentially excluding Russia.
But if the capacity of the pipeline is expanded, which the pipeline has been designed to do — up to 20 billion cubic meters through additional compressor stations along the route — other companies, including Russia’s Gazprom, could reserve space.
Activists — and Five Star leaders — have said that they opposed the pipeline because it resulted from shady business deals and presented environmental risks.
They said the pipeline — which is nearly complete in Greece and Albania and was built by companies including the British oil giant BP PLC and Italy’s state-owned gas company, Snam S.p.A. — was uprooting 1,600 olive trees and wouldn’t bring down gas prices because stabilized prices and contracts would require the sale of gas whether people used it or not.
Michele Emiliano, the president of the Puglia region and a magistrate with links to law enforcement, said in an interview that the No TAP movement was “probably infiltrated” by antiglobalist forces, such as the radical Black Bloc, which have at times turned violent. But he rejected the suggestion that there was any Russian involvement.
“Sincerely, we have the impression that the Russians want to send their gas into TAP,” he said. “And that they aren’t against it.”
Mr. Emiliano, a member of the Democratic Party, advocated an alliance with Five Star, which he said was “elected to stop TAP” but is having trouble finding the courage to tell its supporters that it won’t.
He said he supported the pipeline, in part because it freed Italy from Russian influence, but he wanted it moved to an industrial zone farther north in Brindisi rather than having it arrive “on one of the most beautiful beaches we have in Apulia.”
Instead, he said, out of pure “stupidity,” the private consortium running the project put it in the only place where environmental concerns were legitimate, as was the fear of sunbathing on top of a tube carrying more than a billion metric tons of gas.
“Even if usually they don’t explode,” he said, “some explode.”
The consortium behind the pipeline has sought to allay concerns, arguing that San Foca presents the least environmental impact, including Brindisi.
“We’ve gone door to door to explain to people the reality and reassure they can put their umbrellas down like they’re used to,” said Davide-Maria Sempio, a local spokesman for the company in Lecce. “They will not even realize there’s a pipeline buried 15 meters under the beach.”
Some residents are on their side. Elavio Spagna, 77, walked out of the Grotta della Poesia, a picturesque natural pool down the road, with a bucket full of breams.
“Italy is already full of tubes all over the place,” he said. “Why not here?”
In town, across the street from the mayor’s office, Federico Giannone, 36, sold fish taken from the sea and said he worried the waters would be endangered by the project. He said he thought he had an ally in Five Star. Now, he wasn’t sure.
“Five Star was against it, and now that they are in power they are not sure,” he said. “The opinions of politicians are like the wind.”