The year 2020 was meant to be a relatively quiet time in Europe’s largest economy.

With regular elections only scheduled for the city state of Hamburg, where the centre-left remains strong and the far-right Alternative für Deutschland party (AfD) is projected to get an underwhelming 7% share of the vote, Angela Merkel’s last full year in power promised to be a stable pathway into her political retirement. A good time to focus, at last, on urgent geopolitical challenges: Trump, China, the eurozone.

Instead, the decision by some delegates of her Christian Democratic Union (CDU) in eastern Germany to defy a party ban on cooperating with the AfD did not only lead to the resignation of Annegret Kramp-Karrenbauer, the chancellor’s designated successor, but also ripped up all existing plans for what Germany’s post-Merkel era might look like, or when it will start.

“It won’t be long now until we have fresh elections,” the former Social Democrat (SPD) deputy chancellor Sigmar Gabriel told the tabloid Bild on Monday. “We are currently witnessing the end of Germany’s second large big-tent party.”

﻿In terms of strategy, the debate inside Merkel’s party over the coming months will be about whether the rise of the AfD is best dealt with by shunning the far right completely, or whether to countenance cooperations at regional levels – even if for now none of the contenders are likely to propose a power-sharing deal at federal level, as the Austrian chancellor, Sebastian Kurz, did with the far-right Freedom party.

At the root of this debate, however, is also a wider problem about the unity of the conservative party that has governed and defined the country through 50 of the last 70 years. Merkel’s party in its present form is a post-reunification fusion of the western CDU, defined by staunch Rhineland Catholics such as its towering leaders Konrad Adenauer and Helmut Kohl, and an eastern offshoot that supported and voted with the Socialist Unity party in the de facto one-party state.

After the fall of the Berlin Wall, the CDU was swiftly fused into one party and its ideological inconsistencies covered over – but they could now come back to haunt it.

“Under Kohl, the CDU’s headquarters dealt with the remaining left-leaning tendencies of its eastern branches by parachuting in western Christian Democrats to head the party in the eastern states,” said Gero Neugebauer, a political historian at Freie Universität Berlin. “That strategy used to work – it no longer seems to work now.”

If the defiance of red lines by CDU politicians in Thuringia exposed Kramp-Karrenbauer’s lack of authority, her successor is likely to face similar tests of strength: in Saxony-Anhalt, where there are elections in June 2021, CDU leaders have already said they would consider forming a minority government with the AfD.

Some German commentators believe the only way for Kramp-Karrenbauer’s successor to gain the authority necessary to face such challenges is to not only step out of Merkel’s shadow, but to push her out of the sun altogether.

“All candidates who now step forward should really combine their candidacy with a call for fresh elections,” said Melanie Amann in Der Spiegel. “There are therefore only two logical ways out of the current impasse: in order to survive, the CDU will have to convince a chancellor with record-level popularity ratings to step down. Or this chancellor will have to step down out of her own accord.”

The future of the CDU also throws up speculation about possible coalition-building after the next election. The resurgent Green party, currently second in national polls, will be watching debates among conservatives closely to work out whether it can still consider forming the country’s first conservative-green coalition government without a Merkel figure as a moderating influence.

Katrin Göring-Eckardt, the Green party group leader in the Bundestag, warned Christian Democrats against veering to the right. “Let’s hope the CDU will show us that a Christian Democratic party won’t allow itself to be humiliated by an extreme-right AfD.”

The co-leader of the leftwing Die Linke party, Katja Kipping, bemoaned the demise of Kramp-Karrenbauer, saying she had “demarcated the CDU against the right and thus saved its soul”.

For the rest of this year the world will have to get used to an inward-facing Germany, unlikely to stray outside of its comfort zones.