On Monday morning the oldest German political party, the Social Democrats (SPD), will awake to disastrous local election results, unsure what to say. This should come as no surprise because it hasn’t known what to say for the past seven months.

It has moved so far from their left-of-centre past that it looks like becoming an electoral irrelevance. For those British Labour rebels who are critical of Jeremy Corbyn’s leftwing revolution, there is a warning here of what can happen when a party loses track of its purpose.

Germany faces its biggest turmoil since the post-unification years and after the elections a new political landscape is expected. The youngest German party, the far-right Alternative for Germany (AfD), is likely to celebrate a big victory, and Angela Merkel’s ruling CDU will have lost a lot of voters. But it will be the old aunt, the SPD, that has the biggest electoral hangover. Even if they win the state of Rheinland Pfalz, where they currently govern alone, there are still two big disasters on the horizon: the elections in the eastern state of Sachsen-Anhalt and in Baden Württemberg in the west; in both the SPD is a governing partner. On Monday they are likely to be left as a minor party with around 15% of the vote, in fourth place behind the CDU, the AfD, the Green party in the west and the Left party in the east.

It’s a big drama. In 14 of 16 federal states, the SPD is part of the government; in nine of them, head of state. So historically it has been not only the oldest but also the most powerful party. Not for much longer. One reason is that all other parties, apart from the AfD, now speak like Social Democrats when it comes to the hot topics of gender equality, racism and immigration. Left and right have both shifted to the centre, a space the SPD used to occupy, so it is left with nowhere to sit. Currently it keeps staggering from one policy to another, with no clear direction.

Angela Merkel has placed her CDU, formerly known as a conservative party, a little left of centre and she is still well-respected because her politics are perceived as distinct and consistent. Her famous one-liners – “we will manage that” and “nothing will be closed here at all” – are striking in their simplicity. Next to her, the Social Democrats come across as clowns.

Andrea Nahles, the secretary of labour, seems intent on saying exactly what voters don’t want to hear from a Social Democrat: “Basically, I am a conservative.” And the vice-chancellor, Sigmar Gabriel, twists himself in knots to the point where it’s unclear if even he knows what he is trying to say. When he visited Heidenau, where the first clashes between militant demonstrations and police took place over refugees, he managed to make even rightwing militants look smart by playing to mob mentality.

His next intervention was to say that it was up to German voters to decide how many refugees the country should take in. This new-found love of direct democracy was a surprise – Gabriel had never thought to ask voters how much the minimum wage should be or how much the government should spend on football for public television. And just as it seemed his desperation to attract rightwing votes could sink no further, last week he proposed a new care programme for German citizens – to demonstrate that the government was not just concerned with the wellbeing of refugees.

The SPD could be facing the same situation as Merkel’s previous coalition partner, the FDP: first it was voted out of state governments, then out of the national parliament.

The problem is whether anyone would care? Since the SPD government of Gerhard Schröder the party has been hardline even on social issues. It was the SPD that created the highly controversial Hartz-4-programme, slashing benefits for the long-term unemployed, which was even criticised by the UN. Now the SPD is a nothing, an empty shell of a party. And being a nothing at a time when the far right is growing is not something anybody wants to cheer for. The SPD is left to hope that the hysteria of the AfD politicians fades before they do.

Perhaps – looking at the history of rightwing parties in the last 25 years – they will get lucky.