BERLIN — The shock decision of Angela Merkel’s heir apparent to quit as leader of Germany’s largest party thrust the country’s politics into disarray Monday, reigniting both the race to inherit the chancellor’s mantle and a battle over the direction of the conservative establishment.

Annegret Kramp-Karrenbauer, who took over from Merkel as leader of the Christian Democrats (CDU) little more than a year ago, announced her plans to step down during a meeting of the party’s executive committee on Monday morning. The move followed days of intense criticism over her handling of a controversy surrounding the collaboration between conservative lawmakers and members of the Alternative for Germany (AfD) to elect a new leader of the eastern state of Thuringia.

Kramp-Karrenbauer laid the blame for her fate, at least in part, on her mentor Merkel, saying that separating the positions of chancellor and party leader “weakens the CDU.”

Kramp-Karrenbauer said she would remain as leader until the party settles on a candidate for chancellor, a process that could take until the end of the year. The big question is what happens once the new chief is selected. Given Kramp-Karrenbauer’s experience, it seems unlikely her replacement would accept the party leadership job without the chancellery. In other words, Merkel may have to go a year ahead of schedule.

The Thuringia affair, which renewed a debate over whether mainstream parties should ever cooperate with those on the far right or far left, served as the immediate trigger for Kramp-Karrenbauer’s resignation. But the CDU leader had been under fire for months amid a string of missteps, prompting many in the party's old guard to question her suitability for the chancellorship — the most powerful political job in Europe.

If Merkel has proven one thing during her long reign, it’s her consistency; once she makes a decision, she rarely backs away from it.

“I’ve been thinking about this decision for some time now,” Kramp-Karrenbauer, 57, said at a news conference in Berlin. She said she plans to remain defense minister, a job she took last summer.

Merkel's choice

With Kramp-Karrenbauer, the former premier of the small Saarland region, Merkel believed she could install a successor whose moderate political views hew closely to her own. She choreographed Kramp-Karrenbauer’s ascension, first making her the CDU’s secretary-general before backing her as party leader.

With that plan now in tatters, the prospects of the two men Merkel hoped to block from succeeding her —Health Minister Jens Spahn, 39, and Friedrich Merz, 64, a prominent former MP and longtime Merkel foe — have been rekindled. Both are on the right of the party and haven’t shied from criticizing the chancellor for her policies on migration and areas such as social welfare, where they believe Merkel has steered the party too far to the left.

In right-wing CDU circles, news of Kramp-Karrenbauer’s resignation was seen a welcome chance to reposition the party.

“It’s time to bring Frau Merkel’s years-long left-wing course to an end,” said Alexander Mitsch, a CDU member who leads the so-called Values Union, a right-wing group.

Merkel, who has retained her authority despite relinquishing the CDU’s leadership and ruling out another term as chancellor, is likely to do whatever she can to keep the right wing from succeeding.

In meetings with party colleagues in recent months, Merkel, sensing Kramp-Karrenbauer's flagging fortunes, subtly promoted Armin Laschet, the leader of the state of North Rhine-Westphalia, CDU insiders say.

A moderate like Merkel, Laschet would also have the weight of Germany’s most populous state behind him.

But with Germany’s greatest political prize up for grabs, others are likely to raise their hands as well.

In Thuringia, the AfD overtook the CDU to place second behind the leftist Die Linke party in October, setting the stage for last week’s controversial election.

Indeed, the party’s crisis could even prompt Merkel to rethink her decision to exit the political stage. For all of the criticism of her in her own party in recent years, she remains Germany’s most popular politician, a reality that even her detractors in the CDU can’t ignore.

For now, that prospect remains unlikely. If Merkel has proved one thing during her long reign, it’s her consistency; once she makes a decision, she rarely backs away from it.

Course in question

Whether she can convince her party to maintain her centrist course is another matter. As the upheaval in Thuringia in recent days has illustrated, the emergence of a strong far-right political force has backed the center right into a corner. Many blame Merkel, and in particular her decision to allow a million refugees into the country in 2015, for fueling the AfD’s rise.

The party is particularly strong in Merkel’s home region, the former East Germany, where the far right has consistently won about one-quarter of the votes in recent regional elections.

In Thuringia, the AfD overtook the CDU to place second behind the leftist Die Linke party in October, setting the stage for last week’s controversial election of a new state premier by the legislature. Most observers expected the leftist candidate to prevail, but the CDU joined the AfD in backing the candidate of the liberal Free Democrats (FDP), the smallest party in the legislature. What followed was a firestorm of outrage and accusations that the CDU and FDP had jumped into bed with fascists.

Amid the outcry, Kramp-Karrenbauer called for a new state election — a demand she didn’t have the power to enforce, further eroding her authority. The local CDU refused to follow her instruction.

The episode offered an urgent reminder of how the fracturing of Germany’s political landscape amid the rise of the far right threatens to bring the whole system of coalition-building to a halt.

The CDU leadership has said it rejects any form of cooperation with the AfD or Die Linke. But as Thuringia illustrated, maintaining those red lines has become increasingly complicated.

The CDU denies there was any formal cooperation with the AfD, insisting the two parties just happened to support the same candidate from the FDP. However, if just two CDU legislators had supported the leftist candidate in the secret ballot for premier, he would have won, allowing the CDU to escape accusations it had learned nothing from the Nazi era and was opening the door for a return of fascism.

Right-wingers restless

Many in the CDU are convinced the only way to right the party ship is for it to re-embrace its conservative traditions. Merkel’s internal critics are convinced the CDU could have held the AfD challenge at bay if the leadership had done more to reassure conservative members.

During her 14-month tenure, Kramp-Karrenbauer tried to do just that, but often bungled the execution. Just after getting the job, for example, she made a joke about gender-neutral bathrooms that many found offensive. On more substantive issues, such as migration policy, she often sent signals about where she stood — a reflection of the difficulty she faced in remaining loyal to Merkel while also showing she had her own views.

Indeed, Kramp-Karrenbauer’s biggest challenge was escaping Merkel’s shadow. Parodied by some as the "mini-Merkel," Kramp-Karrenbauer struggled from the outset to prove she possessed the gravitas for the role.

After insisting for months she wanted to focus on running the party and didn’t want a ministerial portfolio, she decided over the summer to take the position of defense minister vacated by incoming European Commission President Ursula von der Leyen.

There too, she had a rough start. After the U.S. decided to withdraw from Syria, Kramp-Karrenbauer suggested Germany work with allies to set up a “security zone” to protect the local population. Though her intentions were noble, she lacked a clear plan on how to undertake such a mission. In risk-averse Germany, where most remain skeptical of military engagement, the proposal was panned and critics accused Kramp-Karrenbauer of being both incompetent and naïve.

The division within the CDU has manifested itself with the emergence of new factions within the party.

Reeling from such criticism, she put her job on the line at a party convention in December, offering during a 90-minute speech to the party faithful to “end things here and now” if they didn’t share her vision for Germany’s future. Delegates responded to her emotional appeal with a long standing ovation, signaling a reprieve.

But Kramp-Karrenbauer’s weakness opened the door for Merz and others to challenge her authority behind the scenes, sparking a debate over who should be the party’s candidate for chancellor next year.

The CDU’s tradition has been to nominate the party leader as chancellor candidate.

Though Merz, a former senior CDU official whose political career was cut short by Merkel's ascent in the early 2000s, holds no formal party office, he retains strong backing among arch-conservatives.

The division within the CDU has manifested itself with the emergence of new factions within the party, Mitsch's Values Union and another known as the “Union of the Center,” which supports Merkel’s course.

At December’s convention, Kramp-Karrenbauer tried to bring the two sides together, stressing that she represented the entire party and didn’t want to be pigeonholed.

“There isn’t Values Union or a Union of the Center, there’s just one union of values, the Christian Democratic Union,” she said to loud applause.

At the convention, Merz shied away from a direct confrontation over the party’s orientation, but proved prescient about the turbulence the party has experienced in recent weeks.

“We’re at the beginning of this process, not the end,” he said.