Bonn’s Bundeshaus in 1992.

Germany’s center-left made a tortured decision last weekend to play second fiddle, yet again, to Angela Merkel’s center-right bloc.

The move ends months of political deadlock in Berlin. But to understand why the troubles of the center-left may persist, look to Germany’s old capital.

It was in this tranquil Rhineland city that the Social Democrats helped rebuild democracy after the fall of the Third Reich in 1945.

And it was here, in 1969, that Social Democratic Chancellor Willy Brandt launched his Ostpolitik program of rapprochement with the east.

Although nearly two decades have elapsed since the seat of government returned to Berlin, the Social Democratic Party remains a creature of old Bonn. Provincial in outlook despite a pro-Europe agenda and unable to expand beyond a dwindling demographic base, the party — Germany’s oldest — has not adapted well to the challenges of a modern, multicultural nation.

“It remained kind of a West German party,” said Andrew B. Denison, director of Transatlantic Networks, an institute outside the old capital. “How does Bonn look at the world? Its aspirations were for unity and diversity, but you see that the Social Democrats haven’t figured out how to connect to East Germans.”

The headquarters of the German telecommunication giant Deutsche Telekom AG in Bonn. (Hermann J. Knippertz/Associated Press)

The party limited its own appeal when, after the Berlin Wall fell, it blocked former members of the East German Communist Party from joining its ranks — in line with its anti-communist stance, which stiffened in Bonn. The remnants of that East German party grew into the Left Party, which now competes with the Social Democratics for votes.

The threat, though, comes from more than one direction. By promising social protection, the far-right Alternative for Germany has made inroads into blue-collar bastions.

Squeezed on all fronts, the Social Democrats mustered just over 20 percent of the vote in the inconclusive federal elections last fall. Particularly worrying for Germany’s center-left, only 23 percent of workers supported its candidates, according to an exit poll, with the party losing the most support in areas scarred by joblessness.

“Politics is successful when you show people you can give them a stable base for their life,” said Ulrich Kelber, the Social Democrat representing Bonn in the national Parliament. “Social democracy is not able to do that in Europe these days.”

Beethoven monument at Muensterplatz in Bonn, Germany. (Ullstein Bild/Getty Images)

Some in the party’s left wing say the “grand coalition,” in place for eight of the past 12 years, is to blame for forcing a center-left party to countenance conservative policies. This is the position of Kevin Kuehnert, the 28-year-old leader of the Social Democrats’ youth wing, who opposed the coalition deal.

Alexander-Frank Paul, the party’s vice chairman in Bonn and a reluctant supporter of the coalition, said the Social Democrats failed to advertise their triumphs within previous governments, such as a higher minimum wage. Rather than revamp its policies, he said, the party should adapt to changing patterns of political engagement, such as declining membership in trade unions, long a bedrock of partisan loyalty.

The small capital, Paul said, forced politics to operate locally, as debates spilled out from the Bundeshaus, the seat of parliament from 1949 until 1999, into nearby bars. “Berlin could learn from Bonn that you have to take time to make politics familiar to people,” he said.

But familiarity bred insularity in the city denigrated by John le Carré as “a small town in Germany” in his 1968 spy novel of the same name. In Bonn, he wrote, “movement has replaced progress, and whatever will not grow must die.”

The prophecy has not come to pass. As government institutions moved out, Bonn’s population grew. It shed its reputation as the “Hauptdorf,” or capital village, and attracted service giants such as Deutsche Telekom, the parent company of T-Mobile, where Paul, 35, works as a product manager.

The 30-story high-rise designed for parliamentary offices by Egon Eiermann, a functionalist and one of Germany’s most renowned 20th-century architects, now houses United Nations institutions. Last fall, Bonn played host to the U.N. Climate Change Conference — and became a site of reckoning with President Trump’s retreat from the world’s fight against global warming.

Beethoven’s birthplace, where government structures rendered in steel and reinforced concrete rose among medieval chapels and Baroque palaces, is now the site of innovative medical research; it boasts museums and concert halls. It is at once a node in a globalized world and a minor city of roughly 325,000, about the size of Riverside, Calif. 

The postwar capital illuminates some of the forces — from the rise of the service sector to the confrontation between globalization and small-town life — that distinguish contemporary Germany from the Bonn years, flummoxing the center-left.

“The separation of society can be seen in parts of Bonn,” said Kelber, Bonn’s representative in Berlin. In Bad Godesberg, an old spa town incorporated into Bonn in 1969, Muslim immigrants moved in beside the well-to-do, creating tensions and, Kelber said, “a feeling that things have gotten worse.”

Karsten Voigt, a longtime Social Democratic member of Parliament who then spent more than a decade handling German-American relations in the foreign office, said the return of the capital from Bonn to Berlin dramatized Germany’s transformation from a ward of international institutions to a global actor shouldering foreign problems. This has challenged the Social Democrats, he said, whose preference for internationalism runs counter to their “practical commitment to people who feel endangered by the arrival of the outside world.”

The two can be reconciled, said Stefan Berger, a historian at Ruhr-University Bochum, in “an alternative vision of globalization,” one that opposes “the downward spiral on wages” without vilifying international commerce. The Social Democrats, he said, should return to a method articulated by Brandt in his first speech as chancellor before the Bundestag in Bonn.

Brandt pledged: “We want to risk more democracy.”

The Social Democrats could seize this moment, Berger said, to revive a more robust brand of politics that fizzled out here, in a small town in Germany.