DUBNICA, Slovakia — Inside the hulking arms factory, dozens of workers delicately fit fuses inside the tips of the 155-millimeter artillery shells that are in insatiable demand in Ukraine’s war.

But even in this town, established around the arms industry before World War II broke out, the deliveries are divisive.

“It’s fuel on the flames,” said Samuel Prekop, 19, as he sat with his family in a nearby square, voicing objections shared by a growing majority of Slovaks.

Fanning polarization across Slovakia is Robert Fico, a socially conservative left-wing populist and two-time former prime minister, who has risen to the top of the polls once again while promising to end military aid to Ukraine and veto “pointless” European Union sanctions on Russia.

For the European Union, a Fico comeback in elections this fall could mean another veto-wielding crack in its political unity in the face of Russian aggression. It could also renew the potential for an authoritarian slide that further challenges the bloc’s democratic ideals.

Fico, who was forced out of office five years ago after the murder of a journalist who had been investigating his finances, is seeing a resurgence that mirrors a populist revival in several countries across Europe. The far-right Alternative for Germany is now polling on par with the ruling Social Democrats, and Austria’s Freedom Party is that country’s leading political force. In Spain, the ultraconservative Vox party may be a kingmaker in next month’s snap elections.

Fico is “surfing a wave,” Milan Nic of the German Council on Foreign Relations said. “Support for populists is now up. There is a crisis in living costs and the lower social strata people are struggling to make ends meet. It’s an environment where you can mobilize resentment.”

Fico is also benefiting from Slovakia’s political turmoil. The country’s westward looking, pro-Ukrainian governing coalition, already facing criticism of its handling of the pandemic, was beset by domestic interparty bickering and collapsed in December but limped along until May with a minority cabinet.

In Slovakia, trust in state institutions is at a low, according to polling by think tank GlobSec, with government trust at just 18 percent.

That frustration has helped to eat away at support for Kyiv, Nic said, because contributions to Ukraine are associated with the country’s unpopular leadership.

Slovak President Zuzana Caputova and her allies say a Russian disinformation campaign also has taken root, amplified by Fico and other opposition politicians.

“It’s a perfect storm,” interim foreign minister Miroslav Wlachovsky said. He spoke in an interview in Bratislava, Slovakia, just two weeks into his new job, appointed as part of a technocratic government charged with steering the country until the September elections.

“Certain historical affinities and a certain naiveté about Russia is played together with the cynicism and opportunism of the Slovak political elite,” he said. “Including former prime minister Fico.”

Only 40 percent of Slovaks say Russia is primarily responsible for the war in Ukraine, while 34 percent blame the West for provoking Russia, according to a March poll by GlobSec. That same survey found that 58 percent of Slovaks would vote to stay in NATO, compared with 72 percent a year earlier, when the war in Ukraine contributed to a surge in support.

On the question of arms for Ukraine, an E.U.-funded survey conducted by the Bratislava Policy Institute found that 70 percent of respondents were against supplying weapons. And an Ipsos survey found that 60 percent of Slovak respondents were against donating MiG-29 fighter jets to Ukraine. Among supporters of Fico’s party, that figure rose to 92 percent.

For his part, Fico has compared a NATO battlegroup in Slovakia to Nazi soldiers and described the war in Ukraine as a conflict between the United States and Russia. He said Ukraine being allowed to join NATO would guarantee World War III.

In a meeting with Fico in April, U.S. Ambassador Gautam Rana said he urged the opposition leader not to ally with Russian President Vladimir Putin, suggesting that doing so would be like appeasing Adolf Hitler.

Within the E.U., some officials and diplomats voice concern about a leader who might align with Hungarian Prime Minister Viktor Orban in obstructing aid for Ukraine and in blocking sanctions on Russia.

“We have to keep unity on the security situation and Russia,” Zilvinas Tomkus, Lithuania’s Vice Minister of National Defense, said. He mentioned a recent meeting of European defense ministers on Ukraine, during which Hungary blocked an aid package. “The problem is we send this ambiguous message to our societies and to Moscow, and Moscow can exploit this message, that there is no unity among European allies.”

“If all of us were to do what Viktor Orban is doing, there would be no independent Ukraine anymore, because they would have no ammunition or weaponry to defend themselves,” Wlachovsky said.

Whether Fico can return to power is still far from certain. His lead in the polls comes with 17 percent of the vote, enough to win an election, but he would still be required to form a governing coalition. Second in the polls is the party of Peter Pellegrini, another former prime minister who split with Fico’s Smer party three years ago and would lose his political raison d’être in forming a coalition with him.

That leaves the extreme right Republica, which is polling at about 8 percent, and a governing coalition likely dependent on whether smaller parties get into government.

If Fico does find his way back into high office, there would be a further question of just how much of his rhetoric against NATO and arming Ukraine would hold firm. After campaigning on a promise to withdraw Slovak troops from Iraq in 2006, Fico carried out that pledge, branding the war “unjust and wrong.”

Fico and other officials from his Smer party were not available for interviews with The Washington Post, but Juraj Blanar, the vice president of the party, responded to written questions. He said that if the party returns to power, it will support Slovakia’s continued NATO membership but would evaluate sanctions “on the basis of the effectiveness of the proposed sanctions in achieving the intended goals and especially on the basis of the economic and social impacts of the sanctions on Slovakia.”

Nic cast doubt on the notion that Fico would be another Orban, on the basis that the fragmented world of Slovak politics wouldn’t grant him as much clout as the Hungary leader enjoys. “Whatever government will be formed, it will be very domestically focused,” Nic said, though he added that it would likely include an end to visible military support for Ukraine.

While Blanar said Smer intends to end arming Ukraine from Slovakian stocks - already depleted through donations - he said it was too early to comment on contracts.

For now, Slovakia is rapidly ramping up its arms production to meet the demands of the war. Last month, the government announced plans to increase the production of 155mm artillery shells fivefold over the next two years.

“We are trying to do as much as we can,” said Marian Majer, deputy minister of defense, “to sign contracts and also make sure the contracts can’t be reversed very easily in the future.”

The Washington Post’s Ladka Bauerova contributed to this report.