By Madeline Chambers
BERLIN (Reuters) - Germany's Social Democrats (SPD) may look reinvigorated with a new leader, Martin Schulz, set to take on conservative Angela Merkel in September's election, but their chances of leading a left-wing coalition to oust the chancellor remain slim.
The surprise leadership switch has given the SPD a psychological boost by ending months of dithering and installing a tougher opponent for Merkel than Sigmar Gabriel, who has been her deputy since 2013. A poll on Wednesday put Schulz's personal approval level with Merkel's at 41 percent.
Yet the euphoric welcome for the former European Parliament president at SPD headquarters after he was catapulted into the chancellor-candidate role on Tuesday, and a spike in membership applications, cannot conceal some uncomfortable facts.
Trapped as junior partner in Merkel's coalition, the SPD trails the conservative bloc by 15 points, has lost 10 million voters in a decade, and is failing to capitalize on Merkel's vulnerability on migrant policy.
The main winner is the anti-immigrant AfD, which has already attacked Schulz as a symbol of EU bureaucracy.
"It will be tough for Schulz, as Gabriel was not the only problem; the party itself has big problems," said Forsa pollster Manfred Guellner.
Fed up of playing second fiddle in a 'grand coalition', the SPD is desperate to offer an alternative. To that end, it has in the last few months held talks with the environmentalist Greens and the hardline Left party to explore possible alliances.
The 'red-red-green' option, already being tested at the regional level in Berlin, looks tempting -- but tricky coalition maths, decades of bad blood between the SPD and the Left party and a new rightist Greens leadership stack the odds against it.
"There is deep frustration with the grand coalition, but having a new chancellor candidate doesn't help if there is no power option," said Cologne University politics professor Thomas Jaeger.
With both the AfD and the pro-business FDP looking likely to make it into parliament, the SPD, Greens and Left look incapable of mustering a majority.
The latest Forsa poll gives them a combined total of 40 percent compared to 37 for the conservative bloc, and analysts expect another right-left alliance, distasteful as it is to everyone in it.
Furthermore the Greens, who shared power under SPD chancellor Gerhard Schroeder from 1998 to 2005, sound cool on Schulz.
"We don't know what he stands for in domestic policy," co-leader Katrin Goering-Eckardt told Reuters TV.
Last week's election of Goering-Eckardt and Cem Ozdemir as co-leaders was widely seen as a shift to the right for the Greens, who are polling around 9 percent and may now prefer an alliance with the conservatives.
BETRAYAL AND LOATHING
However, bridging the deep gulf between the SPD and Left may be an even greater problem for red-red-green. The SPD lifted a taboo on joining the Left on a federal level only in 2013.
The Left is made up of East German ex-Communists and SPD dissenters in the West who quit over Schroeder's welfare reforms and became disciples of his former finance minister, Oskar Lafontaine, loathed as a traitor by many SPD members.
Lafontaine has gone but his uncompromising firebrand wife Sahra Wagenknecht carries his banner, and is equally hated by the SPD.
She told Reuters TV that she would like nothing more than to find a partner for social policies, but was "skeptical" that its centrist line would change.
Indeed, many Left policies seem impossible for the SPD to countenance, not least its opposition to NATO and to sanctions against Russia over Ukraine, and its demand for an increase in income tax up to a top rate of 75 percent.
On top of all that is the heavy burden of history, seen this month in a scandal over a junior minister named to the Berlin government. Andrej Holm was forced to quit after five weeks for concealing the fact that he had worked for East Germany's secret police, the Stasi, for a few months as an 18-year-old. On a federal level, that issue could be a dealbreaker.
Yet, however difficult the road ahead, the SPD has at least made a start by shaking up the election campaign.
"Schulz euphoria won't suffice for an SPD election victory," wrote Germany's biggest-selling daily, Bild. "But Angela Merkel will have to ... go on the offensive - not her strength."
(Additional reporting by Reuters Television; Editing by Kevin Liffey)