The arrival of the Left Party has radically altered the German political landscape and forced Germany's two main parties to seek unusual coalition partners at the state level.
The possibility that the Left could play a decisive role at federal level when elections are held in 18 months even prompted a former president to call for constitutional change to cope with the unexpected situation.
Chancellor Angela Merkel's centre-right Christian Democrats (CDU) has seen a dramatic drop in support in three state elections this year. Their counterparts in the centre-left, the Social Democrats (SPD), are languishing below 30 percent support nationwide, their base eaten into by the Left Party.
And the CDU's sister-party, the CSU, which has ruled in Bavaria since the war, this month lost ground in local elections, not to the Left, but to a collection of minority local pressure groups.
Germans are evidently losing confidence in the broad-church "Volksparteien" that have dominated the post-war era.
The uncertainty resulting from having five blocs contesting the political field has led former German president Roman Herzog to issue a warning that the changes on the left of the political spectrum could find their counterpart on the right.
Herzog, president for five years from 1994, conjured up the possibility that right-wing extremism could once again find a voice in mainstream German politics.
"A fundamental change has taken place in our system of government," he wrote in the national daily Sueddeutsche Zeitung.
"The possibility of a sixth party, which would not necessarily have to be neo-fascist, can in any case not be excluded," he said ominously.
Herzog warned of the dangers of minority governments, with a chancellor forced to make "the craziest compromises" to push through a legislative programme.
A chancellor in this position would moreover be seen as a lame duck in the foreign arena and in the European Union.
This is clearly not what those who drafted the post-war constitution with its built-in hurdle to cut out fringe parties, had in mind, the CDU politician said.
While Herzog's musings on introducing a two-stage majority voting system similar to that used by France to replace the current proportional system drew widespread criticism, his anxieties on the changed nature of German politics found an echo.
The main parties should seek to reconnect with the electorate "by living up to their names and regaining their credibility," the Mannheimer Morgen newspaper said in a representative comment.
Developments in two of the three elections held at state level this year lent force to Herzog's warnings. No clear majorities emerged, largely because of the votes taken by the Left.
In Hesse, a controversial attempt by the SPD to seek a tacit deal with the Left to get its candidate elected premier by the new state legislature collapsed when an SPD member said she would not play along.
In Hamburg, Merkel's CDU was seeking to form a ruling coalition with the Greens - an unthinkable alliance just a few years ago.
The shake-up caused by the rise of the Left is not the first in post-war German politics, which was characterized into the 1980s by governments led by either the CDU/CSU or the SPD, with the liberal FDP minority party playing kingmaker.
A quarter of a century ago, the Greens burst onto the scene, but new blocs soon established themselves, with the CDU/CSU and the FDP on one side and the SPD and Greens on the other.
After initial horror, Germans soon got used to the homegrown protest that the longhaired Greens represented in the hippy era.
But the Left? Many see the party as a repository for unreconstructed communists from the old East Germany. And memories of the bitterness of the post-war partition remain strong.
There are strong feelings within the SPD that the Left could never be a comfortable bedfellow and that the party should be fought to extinction rather than accommodated.
With federal elections just 18 months away, the traditional party of the German left faces tough decisions.