By Paul Day
MADRID (Reuters) - Spain's Socialists choose their leader on Sunday in a vote that will decide their relevance as a center-left party for next few years and set the tone for the ruling minority conservative government's influence in parliament.
Some 188,000 members of what was until recently Spain's only main alternative to the conservative People's Party (PP) will pick between former leader Pedro Sanchez, Andalusia regional party head Susana Diaz and outlier Basque Country's Patxi Lopez.
Polls show the winner will be either Sanchez, a relative hard liner who has proved he will fight the conservatives' market-friendly, deficit-tackling policies, and Diaz, a moderate who is open to seeking consensus in the split parliament.
Whichever way the vote swings, the party is fighting to prove its relevance in a split parliament that has left it between the right-wing policies of the PP and market friendly Ciudadanos (Citizens) on one hand and the hard-left Podemos (We Can) on the other.
Last year's general elections left parliament torn between the four parties and it was Sanchez's refusal to abstain in a vote to let the PP take the leadership and avoid a third election in a year which led to his ouster at the head of the Socialists.
The move gave Prime Minister Mariano Rajoy another term, but with a minority position that needs opposition support for everything he proposes, from economic reforms to the annual budget.
Sanchez's attempted return is one of defiance, showing he is willing to take a more combative stance than his opponent Diaz by blocking PP proposals, laying the ground for four years of political stalemate and potential sparking an early election.
FRACTURED AND STRUGGLING
The Socialists have suffered the fate of many of their left wing peers across Europe in recent years as party politics is distorted by populist leaders from all sides of the political spectrum, leaving its base fractured and struggling for an identity.
In Spain, part of that political sea change has been due to the arrival of the anti-austerity Podemos, which began as a grass roots movement against the PP's deficit-fighting policies during the prolonged economic crisis.
Since Podemos was founded in 2014, it has taken half of the Socialist's support through the political agitation of Podemos leader, former professor Pablo Iglesias.
"When the Socialists lost their profile as the alternative and became confused with their adversary, the electorate ends up not recognizing it and going for more populist options," Sanchez campaign coordinator Jose Luis Abalos said.
On Friday, Iglesias' party filed a motion of no-confidence against Rajoy. It was seen as a challenge to the Socialists to vote to fight the conservatives, by Podemos' side.
(Additional reporting by Inmaculada Sanz Editing by Jeremy Gaunt.)