With national elections in France and Germany out of the way, and the date for Britain’s departure from the European Union set for March 2019, this year had been billed as a window of opportunity for substantial progress in Europe, said Daniela Schwarzer, director of the German Council on Foreign Relations in Berlin. But every day that is spent in a German limbo narrows that window.
“The window is tight,” said Ms. Schwarzer, who predicted that a government could not be formed earlier than March. “We need to make the most of the progress before the summer break.”
Come fall, much of Europe’s energy will be absorbed by the final leg of the Brexit talks, she said. And inside Germany, a hard-fought Bavarian election would mean Ms. Merkel’s conservative sister party, which has been losing votes to the right-wing, euroskeptic Alternative for Germany, may be in no mood to make concessions on overhauls in Europe.
For Ms. Merkel, securing another coalition with the Social Democrats would give her an opportunity to shape her legacy, most likely on European issues, and to begin grooming a successor.
“It would be her fourth and last term, but her chance to go down in history as a European chancellor,” said Andrea Römmele, a professor of political science at the Hertie School of Governance.
Europe’s future has also been one of the main rallying cries by Martin Schulz, the embattled leader of the Social Democrats, in favor of another coalition — even though he had run against Ms. Merkel on a platform of “never” joining her in government again.
“It’s not just about whether we enter coalition talks,” Mr. Schulz, who served as president of the European Parliament from 2012 until early 2017, told delegates in Bonn. “We are deciding which path our country and Europe will go.”
In the two years since Ms. Merkel opened Germany’s door to more than a million migrants, the country’s political landscape has changed drastically, and much of the chancellor’s ability to forge consensus has eroded.
In the September election, her party, the center-right Christian Democratic Union, had its worst showing since the Federal Republic of Germany was founded in 1949. An earlier attempt to form a coalition government, with the free-market Free Democrats and the Greens, failed after four weeks of discussions late last year.
A second rejection, by another major party, said Henrik Enderlein, a professor of political economy at the Hertie School and director of the Jacques Delors Institute in Berlin, would have amounted to “a vote of no confidence.”
The arrival of the Alternative for Germany in the national Parliament after the September vote has made forming a government much harder: There are now lawmakers from seven political parties, spanning the full political spectrum, and traditional postwar coalitions on the left or right no longer have a majority.
Should the coalition proceed, the Alternative for Germany would become the biggest opposition party in Parliament — one reason so many Social Democrats are opposed to joining forces with Ms. Merkel.
“The future of social democracy is at stake, but the future of democracy is also at stake,” said Johanna Uekermann, deputy leader of the Social Democrats in Bavaria, addressing the party congress on Sunday.
Both the Christian Democrats and the center-left Social Democrats have lost ground to the political extremes in recent years, and the collapse of voter support for the center-left to 20 percent — the lowest level since 1933 — has raised existential fears among Social Democrats.
Governing with their traditional rivals on the right has blurred the lines between the two camps. When the Social Democrats first joined Ms. Merkel’s conservatives in government, in 2005, it still received 34 percent of the vote. After a second stint as a junior coalition partner over the past four years, that share fell to 20 percent.
“This is an existential debate for the party,” said Emmanuel Richter, a professor of political science at the University of Aachen. “The party suffers from an identity crisis. It has no clear voter base anymore, no clear link to those who feel left behind and neglected.”
Going into another coalition with the conservatives would postpone a fundamental debate about the party’s future direction for another four years, Mr. Richter said.
And by then it might be too late. “People think that vote share can’t go any lower, but it can,” he said.
Recent polls show that if new elections had been held this weekend, the Social Democrats would have lost even more ground.
The internal soul-searching was palpable on Sunday in the congress center in Bonn, nestled in the Rhine Valley, where many of Germany’s oldest myths and hero-legends are based. About half of the speakers passionately argued in favor of going into government, and the other half was ardently against.
“We have a responsibility before German citizens who want to feel well governed,” said Stephan Weil, the leader of the Social Democrats in the state of Lower Saxony, where he was recently re-elected governor. “If you’re not on the pitch, you can’t score a goal.”
Marc Dietzschkau, a spokesman for the Social Democrats in the Saxon Parliament, countered: “Voters voted against a grand coalition in September,” he said. “Our mandate is to lead the opposition.”
For those leading the opposition to another coalition, the fight is not over.
“We cannot go into another election campaign where people tell us in the streets: I can’t see any difference between you and the C.D.U.,” said Kevin Kühnert, leader of the Social Democrats’ youth movement, who spent the past week canvassing the country asking delegates to reject coalition talks.
Few experts dare to predict what decision members might make once a completed coalition deal is put before them — or what exactly would follow if they rejected it.
“It is impossible to predict what comes next,” said Ms. Schwarzer of the German Council on Foreign Relations. “This is not how we know Germany.”