With its traumatic and meticulously commemorated past and broadly comfortable present, Germany has long seemed relatively exempt from the forces of nationalist populism sweeping Europe. In Angela Merkel and the Christian Democratic Union (CDU) it is led by bastions of “bürgerlich” (bourgeois or respectable) centrism. Even with the rise of the hard-right Alternative for Germany (AfD) – a Eurosceptic party that has become gradually more xenophobic and extreme – in recent years, it seemed clear that Germany had an unusually robust cordon sanitaire. “Cooperation with the AfD would be a betrayal of our Christian Democrat values” said Paul Ziemiak, the CDU’s general secretary, last November, calling Björn Höcke, a particularly extreme AfD leader, a “Nazi”.

Yet today the CDU and the notionally liberal Free Democrats (FDP) ousted Bodo Ramelow, the left-wing premier of Thuringia, a central German state, and replaced him with a minority administration led by the FDP’s Thomas Kemmerich – doing so with votes of the Thuringian AfD, the very branch of the party led by Höcke. The man termed a “Nazi” by Ziemiak was even photographed shaking hands with Kemmerich. Following the vote Jörg Meuthen, the AfD’s leader, told the Frankfurter Allgemeine Zeitung newspaper that the CDU, FDP and AfD were closer to each other than to the other parties; forming a “bürgerlich” political cluster. The once seemingly sturdy German cordon sanitaire is broken.

How did it come to this? Ramelow had led Thuringia since 2014 at the helm of a coalition comprising his socialist Left Party, the Social Democratic Party (SPD) and the Greens. But the red-red-green alliance fell four seats short of a majority in the state’s election last October. Both the CDU and the FDP refused to support Ramelow, deeming his party – a descendent of the East German communists – beyond the pale and presented Kemmerich as an alternative at today’s confidence vote in the state parliament in Erfurt. The votes of Höcke’s AfD group gave Kemmerich a majority: 45 to 44 votes, with one abstention. The FDP candidate might have rejected the result and disavowed the AfD’s support, but he accepted it. His move is symptomatic of the FDP’s rightwards drift under Christian Lindner, its dilettantish yuppie leader. (Lindner’s sombre claim, upon withdrawing from federal coalition talks with the CDU and the Greens in 2017, that “it is better not to govern than to govern the wrong way” is being much cited on German political Twitter this afternoon).

The consequences will be far-reaching. Most obviously, the news exposes the divides and tensions within the CDU, which has been struggling to hold together a wide electoral coalition bleeding voters to the Greens in big cities in the country’s west and to the AfD in conservative corners of the former east such as parts of Thuringia. Annegret Kramp-Karrenbauer, who took over the CDU’s leadership from Merkel just over a year ago, has tried to straddle that divide: presiding over a party that tries to appear moderate and greenish in places such as Hamburg (which goes to the polls on 23 February) and firmly right-wing in AfD-prone places such as Saxony and Thuringia. The news from Erfurt today is the greatest test to date of this (already wobbly) balancing act. Some in the party have already expressed their distress at the news. The party leadership is now urging new elections. Will the party’s base in Thuringia accept this call?

But other questions are more medium-term. Will this move prompt the SPD to reconsider its alliance with the CDU at the federal level? The centre-left party is miserable in the “grand coalition” with Merkel and its new leadership is sceptical about the pact. Olaf Scholz, the SPD federal finance minister and usually a defender of cooperation with the CDU, was unusually forthright in his response to today’s news: “The developments in Thuringia break a taboo in the history of political democracy in the federal republic… They pose serious questions for the CDU’s federal leadership and we demand rapid answers to them.” It is reasonable to suppose that the main winners of today’s events will be the Greens (the natural home for disaffected liberal CDU voters) and of course the AfD itself, which can point to the new government of Thuringia as proof of its acceptability and a step on the road to full participation in a German state government.

The saga is also part of a bigger, European story. It is often claimed that populist nationalism is rising across the continent. The truth is more complicated. Parties like the AfD did surge in the wake of the eurozone and migration crises but in much of Europe that rise has stalled. In France, Marine Le Pen is doing little better than she was during the equivalent point in the last political cycle. Austria’s Freedom Party (FPÖ) has self-combusted over a corruption scandal last year. Geert Wilders’s Party for Freedom, once the Dutch vanguard of the European hard-right, won no seats in last year’s European parliament election. Matteo Salvini’s Italian Lega suffered a setback in last month’s Emilia-Romagna regional election. Even the AfD’s gains at east German state elections, including Thuringia’s last year, can be seen as a consolidation of political shifts that took place earlier in the previous political cycle, around the peak of the migration crisis in 2015-16; at a federal level, the AfD’s last sustained rise in the polls took place over four years ago.

The real shift is that the line between the nationalist populists and the mainstream is becoming more blurred. This process takes two forms. First, as in Thuringia, old cordons sanitaires are gradually falling away. Spain’s centre-right Popular Party (PP) and Citizens (Cs) govern Andalusia under a pact with the hard-right Vox. The extreme Sweden Democrats (SD), once untouchable, now enjoy the cooperation of Sweden’s centre-right Moderates, whose leader Ulf Kristersson even met with the party’s boss in December for what he called a “constructive conversation” on “important issues for the country, where our parties have similar views”. In Britain’s general election last year, Boris Johnson was helped to his 80-seat majority by the Brexit Party’s decision to stand down its candidates in seats held by the Conservatives. Finland, Austria and Italy have all seen far-right parties wield power in recent years.

A common, bogus justification used by mainstream partners of such extremists is that the alternative is as bad or worse: Spain’s PP and Cs have essentially argued that left-led governments are worse than governments reliant on the far-right; in Thuringia the CDU and FDP preposterously equated Ramelow (a moderate, conciliatory sort of leftist) with Höcke (who has said Germany is “crippled” by its “stupid” culture of Holocaust remembrance).

The second way in which populists and the mainstream are merging is imitation. Centre-right (Austria, Greece, Britain, Spain, the Netherlands, France, the Czech Republic) and centre-left (Denmark and to some extent Austria) parties are adopting and adapting language, talking points and policies from nationalist populists; whether on the EU, immigration, social rights or matters of national identity or history. France’s Les Républicains have become Le Pen-lite. Spain’s PP and Cs imitate Vox’s hardline stance on Catalan separatism. Denmark’s Social Democrats have voted in favour a measure enabling immigration authorities to confiscate jewellery from refugees. In taking the UK out of the EU, the Tories have enacted the flagship policy of their country’s hard-right. The best example of all is Hungarian Prime Minister Viktor Orbán, whose supposedly centre-right Fidesz has become a byword for hard-right illiberalism and nativism; its assaults on the Hungarian judiciary and free press not enough to secure its expulsion from the European People’s Party, the main group of Christian democrat parties such as the CDU.

This distinction – between the rise to absolute power of nationalist populists predicted in certain hyperventilating headlines and the gradual insinuation of nationalist populism into the mainstream – is important. To fight nationalist populism, moderates and progressives need correctly to identity what precisely the danger of it is. That danger is not fundamentally one of a Europe run by Höckes. Far, far more likely – and therefore more worrying – is the spectre of a Europe where Höckes prop up governments, colour their policies and help set the terms of the politically acceptable. It is that Europe that became a notch more likely in Thuringia today.