BUDAPEST — The outcome of Sunday’s Hungarian elections is fairly certain: Viktor Orban, the country’s strongman prime minister, will be reelected, extending the grip on power he has held since 2010.

The question is by how much Orban and his Fidesz party will triumph.

What they want is another parliamentary supermajority. With at least two thirds of the 199 seats in Hungary’s National Assembly, they would have enough votes to continue the dramatic overhaul of the constitution they have begun.

A strengthened opposition, however, could throw a wrench in Fidesz’s plans for further changes, and the ruling party could then be met with a heightened public scrutiny that might demand accountability. For a nominally right-wing party that seeks to dominate both ends of the political spectrum, that kind of accountability could prove devastating, analysts said.

Hungary is in the midst of a divisive election that will decide if the country’s anti-immigrant prime minister gets a third straight term in office. (Griff Witte, Jason Aldag/The Washington Post)

Opinion polls show that Fidesz is likely to emerge from Sunday’s vote as the strongest single party, with at least an absolute majority in the parliament.

But a February by-election the party unexpectedly lost suggested some potential for a significant protest vote. In a municipal constituency that Fidesz won with 61 percent of the vote in 2014, independent candidate Peter Marki-Zay soared to victory with 57.5 percent in the Hodmezovasarhely mayoral race. Critical to his win was backing from a unified band of opposition parties that has been difficult to achieve elsewhere. Turnout also made a difference: In the same constituency in 2014, 36 percent of voters cast their ballots, but this year the figure rose to 62.5 percent.

Voter participation is likely to be crucial in determining the ultimate size of Orban’s coalition, too.

His party has a devoted electoral base whose influence would likely be diluted with a higher number of ballots cast. Furthermore, according to Hungary’s voting system, even if an opposition candidate loses in a particular constituency, the votes that candidate receives are added to a party total.

Some political analysts predict that if 70 percent of voters show up Sunday, Fidesz could emerge a minority in what would then be a rare hung parliament. But there’s slim chance of that. And analysts said a fragmented opposition could easily work in the party’s favor.

Both Fidesz and the opposition parties have focused on get-out-the-vote efforts in the closing days.

“It’s time that we finish with these years,” Bernadett Szel, a candidate for prime minister from the Green party, said Thursday to supporters in Godollo, a suburb of Budapest. “Go to the polls. Don’t let anyone decide for you. At the moment, no one’s voice is heard.”

Orban, meanwhile, has argued that a Fidesz victory is the only way to ensure that the government can “save Hungary” — from migrants, from Brussels bureaucrats and from “Uncle George” Soros, a Hungarian American and Jewish financier whom Orban has cast as a globalist puppet master out to subvert the national interest.

“We need to bring everyone to the polling stations,” Orban said in an interview this week on Echo Television, a local right-wing channel owned by Lorinc Meszaros, an oligarch with ties to Fidesz. “The supporters of Soros will all be there. We have to be there also.”

The latest polls suggest turnout will be higher than in any year since 2002, when 70 percent of voters united to oust Fidesz from its first period in power. Turnout has gradually decreased in the years since Orban came to power in 2010, but 66 percent of voters say they intend to cast their ballots this year, according to Median, a leading Hungarian polling agency.

There is still the concern of gerrymandering. In 2011, the administration drastically redrew Hungary’s electoral map, decreasing the number of districts from 176 to 106. The result was that opposition strongholds were often merged into Fidesz-friendly areas. A prime example is that of central Budapest. The typically left-leaning “Pest” side of the Danube River has now been merged with the right-leaning “Buda” side. In 2014, the first ­election with the new map, the district went for Fidesz in a relative majority.

Agoston Mraz, director of Nezopont, a conservative think tank with ties to the Orban government, called the charges of gerrymandering “a myth of the opposition,” insisting that a current, smaller National Assembly of only 199 seats did not require as many representative districts as the previous parliament of 386 seats.

“Whether it’s gerrymandering or a natural redraw of the borders is a more ideological question, depending on your perspective,” he said, noting that votes for unsuccessful opposition candidates still count toward party totals. “We are not living in the U.S., where in the districts the elections are decided.”

For other analysts, the important question is not what happens Sunday but rather after Orban wins reelection — especially if he wins with a coalition that carries fewer parliamentary seats.

“When you ask what they stand for, they have great difficulties explaining,” said Laszlo Csaba, an economist and former Orban adviser who parted ways with the prime minister after his election in 2010. Csaba is now a professor at the Central European University, a Soros-funded institution Orban has attempted to target with new legislation.

“They won’t have four more years of quiet government — that’s highly unlikely,” Csaba said. “The cynicism — the lack of belief in anything besides your own personal gain — is not good for any government. I would predict trouble ahead.”

Gergo Saling contributed to this report.