Spain's anti-austerity party Podemos and its allies could leapfrog the Socialists in this month's repeat general election to become the country's main opposition, three polls released over the weekend.
Surveys published in El Pais, El Mundo and El Español dailies showed acting Prime Minister Mariano Rajoy's conservative Popular Party coming first, with 27.7-31% of the vote, way short of a parliamentary majority.
That result would be comparable to the 28.7% which the party obtained in an inconclusive December 20 general election that resulted in a hung parliament.
The Socialists, however, would drop from the second to third place, garnering just 20.2-21.6% while Unidos Podemos -- an alliance made up of Podemos and its smaller rival Izquierda Unida -- would receive 23.7-25.6%.
The Socialists have long been the voice of Spain's left, but they have been losing support since the 2011 election that swept the Popular Party to power.
Last December Socialists captured 22% of the vote, just ahead of Podemos, with 20.7%.
Podemos, a close ally of Greece's ruling Syriza party, in May formed an alliance with Izquierda Unida, a coalition led by the country's communist party, to run together in the June 26 elections.
Centrist party Ciudadanos would be fourth with 14-16.6%, according to the latest polls, which is slightly above December's 13.9%.
Podemos' strong showing comes despite the tough stance it took when the Socialists failed to form a left-wing government after the last election. The party, formed just over two years ago, has adopted a more conciliatory tone as the repeat polls loom, dangling the possibility of forming a government with the Socialists.
Podemos, led by pony-tailed university professor Pablo Iglesias, has also been rocked by a swathe of resignations and demotions of top figures amid reports of divisions at the top of the party over strategy.
In a surprising way, Podemos has not lost votes despite its internal crisis, centre-right newspaper El Mundo wrote in an editorial. Iglesias continues to mobilize his followers with a discourse that appeals to feelings much more than to reason.
Over half of all Socialist voters, 51.3% said they were less interested in the coming election, but only 31.8% of Podemos voters felt the same way, the El Mundo poll showed.
If the survey results are confirmed at the ballot box, the Socialists would face a difficult choice. Backing a Popular Party government risks alienating their more leftist supporters. But supporting a Podemos government risks estranging its more centrist voters.
Sanchez has repeatedly ruled out forming a government with the Popular Party because of graft scandals which have tainted the formation while at the same time he rejects many of Podemos' key policy proposals such as a massive boost in social spending.
Spain has been ruled by a caretaker government with limited powers since the December 20 polls which put an end to the country's traditional two-party system as voters fed up with austerity and corruption scandals flocked to new groups.
The four parties which won the most seats were unable to agree on a governing coalition, leading King Felipe to call fresh elections. It is Spain's first repeat poll since the country returned to democracy following the death of dictator Francisco Franco in 1975.