Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

LONDON — At a fiery election rally in Budapest last month, Hungarian Prime Minister Viktor Orban — who seems set to extend his rule after Hungarians go to the polls on Sunday — launched into the latest in a long line of attacks on what has become his favorite foe: the Hungarian-American businessman George Soros.

“We are fighting an enemy that is different from us,” Orban was reported to have said. “Not open, but hiding; not straightforward but crafty; not honest but base; not national but international; does not believe in working but speculates with money; does not have its own homeland but feels it owns the whole world.”

Orban's rhetoric — anti-immigrant and, as many critics have argued, anti-Semitic — would have been consigned to the fringes of Europe's far-right just a few years ago.

Yet in a sign of how mainstream these once-taboo views have again become in parts of the continent, such language is now commonplace for the leader, whose country is a U.S. ally and a member of the European Union and NATO.

Viktor Orban Michaela Rehle / Reuters

The idea that Soros, a billionaire financier and political activist who survived the Holocaust, is pulling the strings of an international network of liberal groups has in recent years become a popular trope for right-wing media, whether in the U.S. or Europe.

But Soros' Hungarian roots have also become an especially useful rhetorical tool for Orban domestically.

He has been able to concoct a grand conspiracy theory that the E.U., U.N., and Soros-supported civic groups are working together to force Hungary to take in thousands of mainly Muslim migrants, thereby weakening its independence, Christian culture and identity.

“In the Hungarian context, it’s a little different,” András Bíró-Nagy, a political analyst and co-director of Hungarian think-tank Policy Solutions told NBC News. “Because George Soros is of Hungarian origin, he is used here as the nasty, Jewish businessman who is building up conspiracy networks against Hungary, who would like to turn Hungary into an immigrant country — this is the rhetoric of the government.”

In what critics denounce as a state-sponsored conspiracy theory with anti-Semitic overtones, the Hungarian government spent $48.5 million on anti-Soros ads in 2017, according to data compiled by investigative news site atlatszo.hu.

Orban's Fidesz party, with a firm grip on the media, dominates the public agenda in Hungary. All polls predict a win for him, though something short of previous landslides, on Sunday.

There is also a slight chance that the fragmented opposition could foil an easy victory and strip Fidesz of its Parliament majority.

A third straight term for Orban could embolden other right-wing nationalists across the continent and expose cracks in the 28-nation European Union.

For some, his electoral campaign has worrying echoes of the darkest period of 20th century history in Europe.

“I don’t want to tell you that anti-Semitism isn’t behind this campaign,” Bíró-Nagy says, “because when you look at the posters, it reminds many people of the propaganda of the 1930s.”

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

An anti-Soros Fidesz billboard in Budapest. Adam Berry / Getty Images file

Political activist, video blogger and filmmaker Márton Gulyás, who has been leading a campaign to coordinate opposition against Fidesz, agrees.

“We have a right-wing government who are openly anti-Semitic, promoting this on billboards and attacking one particular Jewish person,” he said.

Orban, 54, served his first term as prime minister between 1998 and 2002. He steered Fidesz from its more liberal origins toward the center right. But since being reelected in 2010 and 2014 with a huge majority in Parliament, he has become increasingly known for his authoritarian leadership and championing of what he terms "illiberal democracy." He has also been beset by accusations of cronyism, corruption and curbs to press freedom.

However, it was Orban's uncompromising response to the 2015 European migration crisis, when he instigated the building of a fence along the country’s border with Serbia, that really established his anti-immigrant credentials.

“I think he saw the opportunity in the refugee crisis,” Bíró-Nagy said.

“Until the refugee crisis, his image was only an authoritarian populist. He still is. But now this image is complemented with that of the defender of Christian Europe, the defender of Europe from refugees and migrants. He now has an image which can be seen as the model for the European far-right.”

Orban's move further toward the political extremes has also been tactical, Bíró-Nagy said, and an attempt to outflank the controversial, insurgent far-right party Jobbik.

It’s a blueprint that has been echoed by several center-right parties across the continent, and one that has been particularly rewarding for Orban.

“It reflects a strategic calculation they’ve had to make,” Matthew Goodwin, an associate fellow at London-based think tank Chatham House, told NBC News.

“The populist right has won over workers from the left but also, in some countries, has eaten into the right electorate. So they’ve clearly made a decision by emulating a lot of their policy positions. Orban, it seems, has been a highly successful, ultra-conservative politician.”

The political dominance of Orban has also coincided with a weakening of Hungary’s opposition.

While Fidesz has consistently been polling at between 40 and 50 percent in the run up to the election, opposition voters are now split in five or six directions.

A banner against Orban's education policy at a protest in Budapest in March. Peter Kohalmi / AFP/Getty Images file

The opposition has also been hampered by Fidesz’s supermajority in Parliament, which has allowed Orban to implement sweeping constitutional and legislative reforms, including changes to the electoral system from which he stands to further benefit.

Fidesz-led electoral reform in 2011 skewed the system in Orban’s favor, critics say.

This has led activist Márton Gulyás and others to instigate a national tactical voting campaign, which is seen by many as the only hope of uniting the country's disparate opposition and weakening Orban.

Gulyás’ online campaign — The Country For All Movement — has seen activists crowdfunding polls in key constituencies where Fidesz is vulnerable in order to identify the opposition candidate they think is most likely to unseat the incumbent.

Such is the extent of frustration with Orban’s stranglehold on politics that left-leaning voters are being encouraged to back candidates from the extreme right Jobbik in order to defeat a Fidesz candidate. “Me, myself: I consider myself a socialist person. I’m a strongly left-leaning person," Gulyás told NBC News.

“But I’m saying, if there is a chance for a Jobbik candidate in a particular district ... who is not an aggressive, racist guy or woman," he continued, "then you should go with that candidate, because that’s the best or only chance to defeat Fidesz.”

One glimmer of hope for the opposition came in a mayoral by-election in Fidesz stronghold Hodmezovasarhely in February, where Peter Marki-Zay, an independent moderate, Christian conservative surprisingly defeated the Fidesz candidate with the endorsement of a number of opposition parties.

“This was really a game changer in this campaign,” Bíró-Nagy said. “Hodmezovasarhely clearly showed that if the Fidesz candidate has to fight one-on-one with the opposition, then not even Fidesz strongholds are safe.”

But can Orban’s grip on Hungarian politics really be overcome? Bíró-Nagy is cautious, and says that the best the opposition to Orban can hope for is for a strong turnout that could help dent his parliamentary majority.

“The real speculation among observers is whether Fidesz will have an absolute majority, or they will lose it," he said.

"But even if they lose it, it would mean that the far-right, and the left, and the liberal side of the Hungarian political spectrum, would have to form some kind of crisis management government together," Bíró-Nagy added.

“It’s a very difficult scenario for the opposition."