But what was previously unthinkable could eventually become a reality as Angela Merkel's embattled centre-right Christian Democratic Union (CDU) party feels compelled to consider other power-sharing options.
One possibility is an alliance with the fiercely anti-migrant Alternative for Germany (AfD), at least at a regional level.
Local elections in three states in the east of the country where polls suggest that the AfD could become the strongest political force — Saxony, Brandenburg and Thuringia — is forcing the CDU to re-think its stance.
“We should not rule out a coalition” with the AfD, Ulrich Thomas, one of the regional leaders of the CDU in the central state of Saxony-Anhalt, told local daily Mitteldeutsche Zeitung.
“It is not possible now, but we don't know what the situation will be like in two or five years' time.”
For the time being, the CDU's central leadership rules out any suggestions the party could join forces with the AfD, especially in the wake of the murder of local politician Walter Luebcke earlier this month, allegedly by a right-wing extremist.
Signs of weakening
But Saxony-Anhalt will elect a new regional parliament in 2021 and another local CDU leader, Lars-Joern Zimmer, pointed out that voters of his party and the AfD often held similar views and felt themselves to be part of Germany's
Recently, Germany's former domestic spy chief and a member of the CDU's right-wing, Hans-Georg Maassen, also refused to rule out an alliance at national level, saying “you never know”.
On Sunday, the deputy chief of the AfD, Georg Pazderski, suggested that “the united front (against his party) is beginning to crumble”.
“In particular, the CDU base — which has been massively disappointed by its own leaders — cannot be told that the party should be closer to the left than to AfD,” he told the Sunday edition of Welt newspaper.
There is media speculation that the CDU might team up with the environmentalist Greens party, which made significant gains in the recent European elections, in a power-sharing coalition.
But at the head of the CDU, general secretary Paul Ziemiak, 33, has tried to shut down any debate about an alliance with the far-right.
“Just to make it clear to everyone: the CDU strictly rejects any coalition or cooperation with AfD,” tweeted Ziemiak on Thursday.
Nevertheless, Merkel's party is under pressure and, after a disappointing victory in the 2017 elections, is continuing to struggle at the polls.
A survey by broadcaster RTL published Saturday puts the CDU only second with the Greens top and AfD third.
September could prove to be a turbulent month for Merkel's CDU in the regional elections in Saxony and Brandenburg, the AfD's heartland.
The Greens insist any local alliances between the CDU and the far-right would be an obstacle to a possible CDU-Green coalition at national level.
“It would suddenly increase the distance between us,” admitted Greens leader Michael Kellner on Friday.
More worrying for both the CDU and Merkel is the pressure being piled on the Chancellor's favoured successor, Annegret Kramp-Karrenbauer, who is facing increasing challenges within the party.
Kramp-Karrenbauer, who is known in the media as “AKK”, came under heavy fire particularly among younger voters last month when she called for limits to free speech around elections.
Last week, Merkel, 64, criticised her own party, saying it was too “defensive” and not “open enough”.