In the 13 years since its founding, Alternative for Germany (AfD) has established itself as a significant political force — yet it has never been part of any state or federal government. That record is the product of what is widely known as a “firewall”: a refusal by Germany’s mainstream parties to cooperate with the anti-immigrant, far-right party.

That firewall now faces its greatest test after AfD won a landslide victory in Sunday’s election in the eastern German state of Saxony-Anhalt.

Germany’s mainstream parties have long maintained that they would not work with AfD, which the country’s domestic intelligence agency classifies as an extremist group in some regions — including Saxony-Anhalt itself. Any dealings between mainstream parties and AfD carry particular sensitivity given Germany’s Nazi past.

Many Germans had believed their country had developed an immunity to nationalism and claims of racial superiority after confronting the horrors of the Nazi era through education and laws outlawing persecution. That conviction, however, has proven mistaken: like voters elsewhere in Europe and beyond, German voters are increasingly empowering the extreme far-right party. AfD’s rise mirrors a broader shift across the continent, where far-right parties have entered or propped up governments in countries including Italy, the Netherlands, and Sweden in recent years.

AfD rejects accusations that it is undemocratic or even anti-constitutional, and has repeatedly pushed back against the firewall.

The taboo has at times forced other parties into unusual alliances to keep AfD out of power — for example, the three-party coalition spanning ideological divisions that governs the eastern state of Thuringia, formed after AfD emerged as the strongest party in a regional election there for the first time two years ago.

In Germany’s national election last year, AfD recorded the best result for a far-right party since World War II and became the strongest political force in parts of the country. It became the largest opposition party in parliament after Chancellor Friedrich Merz’s center-right Christian Democrats upheld the firewall and formed an unpopular coalition with the center-left Social Democrats.

On Sunday, AfD took 43.8% of the vote in Saxony-Anhalt — more than double its showing in the state five years ago — while Merz’s party lost roughly half of its support.

Merz has strictly ruled out any form of cooperation with AfD in the past, and top officials reiterated that stance on Sunday. But other parties in the newly elected state parliament may be less committed to maintaining the firewall.

The AfD candidate for governor, Ulrich Siegmund, aims to become the first far-right head of a German state government and has already said he will approach all other parties and individual lawmakers in an effort to assemble a governing majority. While Siegmund has rejected the option of an AfD minority government, his party could potentially govern with the hard-left BSW party, which won 5.3% of the vote. The two parties share a Russia-friendly outlook and both oppose immigration, though they disagree on a range of other issues. The BSW — Sahra Wagenknecht Alliance — was founded in 2024 as a breakaway from the Left Party.

On Monday, BSW’s lead candidate in the election, Thomas Schulze, expressed his party’s willingness to help an AfD governor take office in the state parliament.

Forming a government that excludes AfD would require all other elected parties to work together — the CDU, the Social Democrats, the Greens, the Left Party, and the BSW. A five-party coalition, however, would be highly unusual, extremely complicated, and prone to instability.

There is also the possibility that newly elected lawmakers from other parties could defect to AfD — the party would need only three people to secure a governing majority.

Political analyst Volker Resing said AfD may be able to break through the firewall following its strong result in Saxony-Anhalt, with the BSW potentially acting as kingmaker.

“This tiny party could now play a decisive role in determining the future of Saxony-Anhalt,” he told The Associated Press.

Resing said “it is still unclear” whether the parties will join forces on the basis of their common stance toward Russia to overcome the firewall and succeed in forming Germany’s first far-right state government since the end of the Nazi era.

This story was originally featured on Fortune.com.