A week after Antonio Tajani's surprise win as the candidate for the main conservative bloc in the European Parliament, the Socialists are preparing a counter-attack to win back the presidency.

The roadmap to victory, as they see it, involves courting the Greens, lobbying for a Socialist at the helm of the European Council and uniting Europe's left-wing forces.

“The Socialists are in a fighting mood,” said a senior official from the Progressive Alliance of the Socialists and Democrats (S&D).

The early departure of Parliament's current president, Socialist Martin Schulz, who is returning to Germany to pursue a career in national politics, is likely to pit Tajani against his fellow Italian countryman, S&D's Gianni Pittella.

And unlike the last election, the January 17 vote has Brussels in real suspense.

The end of the 'grand coalition'

The suspense in part stems from the fact the Socialists have seemingly abandoned the so-called grand coalition, a 2014 power-sharing agreement with the European People's Party (EPP), under which the presidency was supposed to pass from the S&D to a conservative leader in 2017.

Under the old order, Juncker, Schulz, Commission First Vice-President Frans Timmermans, EPP group leader Manfred Weber and Pittella formed a power trust known as the G5, which allowed the Commission to work with the Socialists to get its agenda through Parliament.

“Pittella was part of the G5 band,” an S&D official said. “He was the greatest defender of the grand coalition."

But last month, a number of Socialist members of Parliament, including French MEP Pervenche Berès, sent Pittella a letter asking him to ditch the deal. “So Pittella completely changed his mind, because he wanted to win,” the official said.

If ALDE doesn’t put forward its own candidate, the liberal group could become Parliament's kingmaker.

According to several sources, Pittella approached several Socialist heads of state, including Hollande and ex-Italian Prime Minister Matteo Renzi, seeking their blessing to end the agreement. "Before he decided to end the grand coalition, Pittella consulted a lot of Socialist leaders who told him, 'go ahead and push it to the limit,'" a senior parliament source said.

Pittella signaled he was dumping the grand coalition when he announced last month that passing the presidency to the EPP would create a “right-wing monopoly in the EU institutions,” given both European Council President Donald Tusk and European Commission President Jean-Claude Juncker belong to the EPP.

Rather than a matter of principle, Parliament sources describe Pittella’s backflip as a political strategy to win the backing of a collection of left-wing MEPs, potentially from the Greens and the European United Left–Nordic Green Left (GUE-NGL), who aren't keen on cooperating with the EPP.

“We are open to chat with Pittella and see what he proposes to end the grand coalition," said a senior official from the Greens, when asked whether they would support Pittella. "But the main point is not the presidency. It is also to ... change the political line.”

To win Parliament's top job, Pittella needs the support not only of a united left-wing bloc and the Greens, but also at least some MEPs in the liberal ALDE group. Guy Verhofstadt, ALDE's leader, has not yet declared whether he will run for the presidency. But if ALDE doesn’t put forward its own candidate, the liberal group could become Parliament's kingmaker.

“The most useful thing for Pittella would be to search for an alliance with the Greens, GUE and a part of the liberals,” said Sergio Cofferati, a prominent Italian S&D member.

The as yet unanswered question is who Schulz will endorse as his replacement. At a news conference last week, he said the power-sharing agreement had been successful in enhancing cooperation between EU institutions at a time of rising populism and Euroskepticism in Europe.

One source said Schulz is lobbying behind the scenes to promote ALDE's Verhofstadt over Pittella.

Tusk in the balance

Several sources also said Pittella is unlikely to give up his aspirations unless he can reach a compromise with the EPP to replace Tusk with a Socialist when his term as Council president ends in May. Several sources said Pittella and the Socialists are discussing three potential candidates to succeed Tusk: outgoing French President François Hollande, former Danish Prime Minister Helle Thorning-Schmidt and Maltese Prime Minister Joseph Muscat.

An S&D official said speculation about the Council's top job was rife in Strasbourg during the Parliament's last voting session.

Few people appear willing to let Tusk go, in part because it would play into the hands of Jarosław Kaczyński, the leader of Poland's Law and Justice party.

“Few people think Hollande, who has lost so much credibility, could make it," the official said. "Thorning-Schmidt -- why not?”

A spokesman for Pittella said the Italian politician “firmly opposed" any suggestion his group was scheming to replace Tusk. Regardless, few people appear willing to let Tusk go, in part because it would play into the hands of Jarosław Kaczyński, the leader of Poland's Law and Justice party. Kaczyński, one of Poland's most powerful people, is anti-establishment, Euroskeptic and Tusk’s Polish nemesis.

Finding themselves again

Beyond political strategy, Pittella appears to see a broader opportunity in ending the grand coalition. According to some on the left, the power-sharing deal has watered down the Socialists' principles. And the party has faced headwinds throughout the Continent.

France's Hollande, facing an imminent defeat, announced he would not contest the presidential elections next year. Italy's Renzi resigned from the prime ministership earlier this month after suffering a crushing defeat in a referendum on constitutional reform. In Spain and Germany, countries with Europe's two biggest center-left forces, the PSOE and SPD have also suffered major losses in recent years.

“Socialists are defeated everywhere,” a senior Parliament official said. “They are seen as the weak link of alliances with the center-right, so the left needs to get into opposition.”

Schulz's departure and the wavering grand coalition have given the Socialists an opportunity to define themselves again.

"For the first time in years, there is a space for the Socialists to fill," the S&D's Cofferati said.