By Noah Barkin and Holger Hansen
BERLIN (Reuters) - The German political landscape is strewn with men who tried to take on Angela Merkel and failed. Sigmar Gabriel, the leader of the center-left Social Democrats (SPD), is working hard to avoid the same fate.
Since the SPD's crushing defeat at the hands of Merkel's conservatives in an election last September, no German politician has racked up as many political wins as the 54-year-old economy minister with keen political instincts and a knack for rousing speeches.
Gabriel's importance lies in the fact that he is holding his party together in the face of Merkel's enduring popularity, a necessary first step towards giving the SPD another crack at power even though it still faces a long haul before voters will buy into that.
In the aftermath of September's loss, he went out on a limb to convince his fractious party to join forces with the chancellor in a right-left "grand coalition", ultimately winning over his colleagues and securing policy concessions from Merkel.
Since the coalition government took power seven months ago, the SPD has dominated the domestic policy agenda, with Gabriel as vice chancellor and minister for economic and energy issues.
He has overseen a reform of Germany's complex renewable energy law, a task that eluded Merkel's previous center-right government. His party has also delivered on policy promises on a minimum wage and pensions.
For the first time in over a decade, SPD officials say, infighting over the party's direction and who should lead it has subsided. In November, Gabriel will become the longest serving SPD leader since party great Willy Brandt - though at five years so far it is a far cry from Brandt's 23-year reign.
"In the party it's clear now, he's the number one," said Jan Stoess, leader of the Berlin branch of the SPD. "With the policies of the new government, he has pacified the SPD. The party is relatively happy now and relatively calm."
This is no mean feat. Ever since former SPD Chancellor Gerhard Schroeder pushed through welfare reforms a decade ago, the party has endured rows between its left and right wings.
It has switched leaders five times since 2004. In the 2009 election, support for the SPD crashed to a post-war low of 23 percent. In September it didn't do much better, with 26 percent.
Gabriel, who was born in the northern town of Goslar and became one of Germany's youngest state premiers at the age of 40 when he took over Lower Saxony in 1999, is a pragmatist who can bridge the gap between left and right.
"You should neither bury (Schroeder's reform) nor treat it like a monument to lay wreaths at every day," he said in 2008.
However, to have a chance of reclaiming the chancellery in 2017 - when he could face Merkel or her successor as leader of the conservative Christian Democrats (CDU) - Gabriel must vault the party back above the 30 percent mark and improve on his personal popularity ratings, pollsters say.
So far, despite his policy triumphs and the newfound party harmony, that hasn't happened. Support for the SPD has barely budged since the vote.
In a Forsa poll this week, 62 percent of voters said they preferred Merkel in a theoretical two-way race for chancellor, compared to just 11 percent for Gabriel, who was dismissively referred to as "Siggi Pop" in the early 2000s when he briefly became the SPD's representative for pop culture.
"Overall, his image has improved," said pollster Matthias Jung of Forschungsgruppe Wahlen. "But Merkel is in another league."
Merkel and Gabriel worked together in her first coalition with the SPD from 2005-2009, when he was environment minister. The 2010 leak of a confidential text message from Gabriel, then leader of the opposition, to Merkel about a candidate for the presidency caused tension, but they have patched things up.
To address what even SPD members describe as a "seriousness deficit", Gabriel, has taken a page out of Merkel's book, by hunkering down, working hard and keeping quiet.
He gets up at 5-6 a.m. and regularly puts in 17-18 hour days, according to his colleagues. He gives fewer interviews.
To soften his image, he has opened up about his personal life, talking about his estrangement from a Nazi father and taking Wednesday afternoons off to pick up his daughter from nursery.
Gabriel, who declined a request to be interviewed for this story, is also shaking things up at the economy ministry, a staid bureaucracy whose influence has waned.
He took over responsibility for Germany's high-profile switch to renewable energy, hiring Rainer Baake from the Greens to lead the reform while he wooed industry by defending it against criticism from Brussels.
Keenly aware that a sound record on economic management will be crucial for success in the next election, the SPD leader has implemented other changes at his ministry.
He has recruited Jeromin Zettelmeyer, a Spanish-born, MIT-educated economist who was director of research at the London-based European Bank for Reconstruction and Development, to run the important economic policy section.
In a sign of Gabriel's desire to have a say in European policy, Zettelmeyer has begun attending preparatory sessions for euro zone finance ministers' meetings previously reserved for chancellery and finance ministry officials.
Gabriel even weighed in on a debate about European Union deficit rules during a visit to France last month.
He is also looking into ways to boost investment in infrastructure and get capital flowing to start-ups, as part of a push to bolster the SPD's image as a guardian of the economy and defender of the middle class. During last year's election, polls showed this was one of the SPD's big weaknesses.
Joerg Asmussen, who moved to the SPD-run labor ministry from a top job at the European Central Bank when the coalition was formed, argues in party newspaper "Berliner Republik" that the SPD must move to the center to win new supporters.
"To emerge from the 25 percent ghetto we need a broader new agenda aimed at the middle class," he wrote. "This is the only way we Social Democrats can hope to claim the Chancellery again at some point in future."
But if Merkel does run for a fourth term in 2017, Gabriel's chances of becoming chancellor may be slim. The "Mutti" (Mummy) of the nation is riding a wave of popularity that is unprecedented in post-war German history.
(This story has been refiled to correct a typo in the second paragraph)
(Additional reporting by Andreas Rinke, Gernot Heller and Madeline Chambers; Writing by Noah Barkin; Editing by Giles Elgood)