BERLIN — German politics were thrust into disarray late Saturday after a surprise decision by the Social Democrats (SPD) to elect a leadership duo that has expressed deep reservations over the party’s participation in Angela Merkel's government.

SPD members elected Norbert Walter-Borjans, a former regional minister from North Rhine-Westphalia and Saskia Esken, a little-known MP from Baden-Württemberg, to take over the beleaguered party, which has been under interim management for six months.

The vote casts doubt on the viability of the so-called "grand coalition" with Merkel's Christian Democrats, which has already come under severe strain amid deep divisions on issues such as taxes, welfare spending and defense, to name but a few.

Walter-Borjans, who campaigned on a promise to demand major spending concessions from the Christian Democrats, said the new leadership’s first priority would be “to define a clear position vis-à-vis our coalition partner.”

The Christian Democrats responded by saying they had no intention of renegotiating the coalition agreement they sealed with the SPD last year. The agreement remained the “basis” for the coalition’s work, CDU Secretary-General Paul Ziemiak said.

After his defeat, Scholz stressed that the most important thing is for the SPD to unite and he pledged to support the new leadership.

Esken and Walter-Borjans beat a rival duo led by Finance Minister Olaf Scholz, who also serves as vice chancellor and was seen as a guarantor of the SPD’s continued allegiance to the grand coalition. While polls leading up to the decision were mixed, many analysts believed Scholz would ultimately prevail given his higher public profile.

Scholz’s loss — he and his lesser-known partner, regional politician Klara Geywitz, won just 45 percent of the votes, compared with 53 percent for Walter-Borjans and Esken — also raises questions about his future as finance minister, the most powerful position in the government after the chancellorship.

While Scholz generally gets high marks as finance minister, many observers question whether he can remain in the important post given that his views on spending — he supports maintaining Germany’s balanced budget — stand in clear opposition to those of the new leadership team.

After his defeat, Scholz stressed that the most important thing is for the SPD to unite, and he pledged to support the new leadership.

“If we are to become strong again, this is crucial,” a stone-faced Scholz told reporters at SPD headquarters in Berlin after the ballot results were announced.

Merkel minority?

A collapse of the grand coalition would likely lead to a minority government led by the CDU and its Bavarian allies, probably under Merkel’s leadership. Though Merkel has made clear her distaste for such an outcome, which would force the government to build coalitions on an ad-hoc basis, she may have no choice. The Bundestag, the German parliament, may not support another candidate for the chancellor post in a minority government.

A failure to agree to install a minority government would force a new election. But with Germany due to take over the presidency of the Council of the EU next July for a crucial six months, none of the mainstream parties wants to risk an election in the short term, arguing it would be too disruptive. Germany’s next regular election is scheduled for the fall of 2021.

Walter-Borjans and Esken, who need to be confirmed by delegates at an SPD convention next week before formally taking over, have signaled they would make the SPD’s allegiance to the grand coalition contingent on the Christian Democrats embracing their plan to spend billions more than planned on infrastructure in the coming years. They also want to raise Germany’s minimum wage to €12 per hour from just over €9 currently.

The CDU opposes a spending offensive both on principle and on the grounds that it would put an end to the government’s recent string of balanced budgets. In fact, the ideas propagated by the SPD duo are so far away from the mainstream of the Christian Democrats that it’s difficult to see where there’s room for compromise.

Saturday’s victory by Walter-Borjans and Esken was the culmination of a process that began in early September.

A decision by the SPD on whether to remain in government is expected to come at next week’s convention.

While a decision to exit the grand coalition might be popular among the SPD’s base, it would risk further damaging the party’s standing in the country at large.

The SPD has been battered in recent years, falling from over 30 percent in the polls in early 2017 to just 15 percent today. Along the way, the party has been distracted by leadership upheaval and hammered in one election after the next.

For all of the tension within the coalition, a majority of Germans say they still support it. It’s easy to see why: During uncertain times in a country that prizes stability above all else, the grand coalition remains the least disruptive option.

Unlike the SPD’s rank-and-file membership, which sent a clear message by nominating Walter-Borjans and Esken to run the party, convention delegates, many of whom are party functionaries, have proved more loyal to the grand coalition.

There’s an outside chance the convention could ignore the membership ballot, which isn’t binding, in favor of a candidate or leadership team of its own choosing. But it would be highly risky for delegates to ignore the will of the membership, especially considering the party’s desperate state.

Many members blame the erosion in support for the center-left party on its participation in the grand coalition, which critics say has forced the SPD to abandon its core social principles in the name of compromise. SPD members also complain that Merkel, as the government's leader, has proved adept at taking credit for their policies and the administration's successes.

Saturday’s victory by Walter-Borjans and Esken was the culmination of a process that began in early September with a dozen male-female pairs vying for the top job.

After generally allowing party mandarins to select the SPD’s leadership in backroom negotiations for more than 150 years, the party, scrambling to reverse it slide, decided to give its members more of a voice.

Members of the SPD establishment, most of whom supported Scholz, didn’t like what they heard. German media’s center-left commentariat was also less than enthusiastic about Saturday’s result.

“A left-wing MP unknown far and wide and a moderately successful, retired regional finance minister at the top of Germany’s oldest party — this isn’t going to go well,” a columnist for Tagesspiegel, a center-left Berlin daily predicted.