MADRID — In May 1879 a typographer called Pablo Iglesias headed a meeting of 25 people in Casa Labra, a restaurant that still stands in Madrid. They agreed to pay regular fees and signed a manifesto opposing all kinds of bourgeois political forces.

It was the birth of the Spanish Socialist Workers' Party (PSOE), the country's oldest surviving political force, which was banned by dictator Francisco Franco but rose from the ashes to dominate the left after the transition to democracy.

Now another man called Pablo Iglesias, a ponytailed politics lecturer aged 37, is making a profound impact on the PSOE — challenging its hegemony of the Spanish left.

The leader of the anti-austerity protest movement Podemos (We Can) is snapping at the heels of the PSOE's telegenic 43-year-old leader Pedro Sánchez, while in a parallel struggle Prime Minister Mariano Rajoy, 60, faces a challenge for conservative votes from the centrist Ciudadanos (Citizens) party led by 36-year-old Albert Rivera.

As a result, pollsters are predicting that Sunday's general election will be the tightest contest in Spain's democratic history and fragment the political landscape like never before.

Most polls still rank the PSOE second after Rajoy's PP, with Ciudadanos third and Podemos fourth. But the distance between the two leftist parties has narrowed dramatically since the campaign began and some even predict that Podemos could overtake the PSOE — which would create a crisis of identity and leadership in the Socialist party.

"If you had asked me two weeks earlier if the sorpasso was possible, I would have answered with an unequivocal no," said Lluis Orriols, politics professor at the Carlos III University in Madrid. "Now I would say anything can happen."

The Podemos leader hit the headlines in 2014 by attacking Chancellor Angela Merkel and advocating a default on public debt; in this campaign, however, he has hardly mentioned German-prescribed austerity. Also On Politico Rajoy’s hometown challenge

Paradoxically, as the competition between the two leftist forces for undecided voters has got closer, and their antagonism more pronounced, they appear to have converged in style and content.

Pundits saw an earlier version of Iglesias in the Sánchez who debated one-on-one against Rajoy on Monday, the prime minister's only TV debate of the campaign. Sánchez launched a brutal attack on Rajoy for corruption in his party and accused him of being a liar and lacking decency.

Iglesias, in contrast, has softened his tone. The Podemos leader hit the headlines in 2014 by attacking Chancellor Angela Merkel and advocating a default on public debt; in this campaign, however, he has hardly mentioned German-prescribed austerity.

"It was no coincidence that I was named Pablo Iglesias," the Podemos leader often tells his audience, explaining that his parents wanted to pay homage to the father of the labor movement — a gesture designed to appeal to disaffected PSOE voters.

Syriza problem

Podemos' strategy has been to portray the PSOE as one half of a thoroughly corrupt 'old regime,' a political force that has betrayed its working-class origins to deliver the same policies as the conservatives.

"It's difficult to present yourself as a leader for a new era of change when your economic guru [PSOE former minister Jordi Sevilla] has just come out of PricewaterhouseCoopers," said Jorge Moruno, responsible for propaganda at Podemos.

At the beginning of the campaign, Socialist leader Sánchez ignored both Podemos and Ciudadanos, presenting himself as the only credible rival to Rajoy in a contest with only two serious contenders — the PSOE and the PP.

The strategy failed when opinion polls began showing Ciudadanos' share of voter intentions rivaling, if not surpassing, the PSOE: no longer the only alternative to Rajoy, Sánchez had to swallow his pride and tackle the newcomers.

The PSOE leader's strategy since then has been to depict Podemos as a communist party, with frequent unflattering references to Greece's leftist leader Alexis Tsipras, whom Iglesias actively supported in his rise to become prime minister. The Podemos leader took part in a rally for Tsipras' Syriza party in Athens — but now doesn't mention his name.

"The example of Syriza in Greece has hit them hard," said Manuel de la Rocha, the PSOE's head of economics. He compares Podemos to the Latin American left that, in his view, has tried to solve complex problems with simple solutions.

The PSOE and Podemos could come under pressure after Sunday's vote to become allies against the right, or even attempt a coalition.

"You can't combat inequality by hammering company profits with taxes," he argued, "because the next day they may have left for Luxembourg."

"There's brutal, global competition, that's how the world works, and you can't change that," de la Rocha added.

An average of polls made by Kiko Llaneras for the online newspaper El Español on Monday put the PP in the lead with 27.4 percent of votes and the PSOE second with 20.7 percent. Ciudadanos and Podemos were both challenging the Socialists for second place, polling at 19.4 percent and 17.3 percent respectively.

The PSOE and Podemos could come under pressure after Sunday's vote to become allies against the right, or even attempt a coalition if the PP falls short of a governing majority and can't get Ciudadanos on board. Their rivalry will continue, however.

Jorge Galindo, a researcher at the University of Geneva, said which party ends up prevailing depends on many factors, such as the regional coalitions Podemos has made in Catalonia, Galicia and Valencia, which bear risks: The promise of an independence referendum in Catalonia, for example, is hard to deliver, and could drive a wedge between Podemos and its regional allies.

Whatever the outcome, the advent of Podemos means the PSOE will struggle to maintain its place as a typical European social democratic force appealing to "the losers of society and the middle classes to sum up 40 percent of the electorate and win elections," said Galindo.