Leading candidates for the European election, Margrethe Vestager, Manfred Weber and Frans Timmermans. | ARIS OIKONOMOU/AFP/Getty Images Timmermans lays ground for left coalition against EPP In debate, Socialist candidate looks to Greens and leftists to break center right hold on top EU posts.

Frans Timmermans, the Socialist nominee for Commission president, used the last major candidates' debate Wednesday to push for a left-wing alliance that could break the center right's monopoly control of the EU leadership.

Overall it was a lackluster debate, in which the candidates struggled to distinguish themselves and offered little clarity for voters about how the EU would respond to rising nationalism or answer aggression by China or the United States.

But on questions about climate change, economic policy and resurgent nationalism, Timmermans sought to portray his Party of European Socialists (PES) as in close harmony with the Greens and the far leftists, and he led his fellow candidates in blistering attacks on Manfred Weber, the German nominee of the center-right European People's Party (EPP).

With less than two weeks to go until the European Parliament election, Timmermans also sought to leave space for a partnership with the new centrist-liberal force that French President Emmanuel Macron is seeking to create to replace the Alliance of Liberals and Democrats for Europe (ALDE) — though ALDE's candidate on stage at Wednesday night's debate, European Competition Commissioner Margrethe Vestager, seemed to steer clear of some of the most heated exchanges.

Still, Vestager also sought to engage Weber, whose EPP now holds the presidencies of the Commission, Council and Parliament, at one point turning to face him directly as she upbraided him for trying to give his party credit for policies that commissioners have together adopted to fight climate change.

However, it was Timmermans, a former Dutch foreign minister currently serving as first vice president of the Commission, who led the charge against Weber and the EPP, and who delivered some of the most pointed and memorable lines.

Responding to a question on climate change, Timmermans praised the efforts by his Socialists, as well as by the Greens nominee, Ska Keller, and the Party of the European Left's Nico Cué, and insisted they could unite a wide spectrum of progressive politicians.

"The three of us already have quite a good record in the last five years in the European Parliament," Timmermans said. "My offer to them is let’s work together in the next five years so that we make sure that the next Commission puts the climate crisis on the top of its agenda and I am sure we will also convince many, many people in the liberal family so that we create an alliance going from [Greek Prime Minister Alexis] Tspiras all the way to Macron."

In perhaps the sharpest exchange of the debate, Timmermans blasted Weber for insisting on painful austerity measures in response to the last financial crisis, and rejecting more moderate economic programs offered by national capitals, including Lisbon. And he accused Weber of taking an even harder line than Commission President Jean-Claude Juncker.

"Manfred Weber said 'no, punish Portugal, punish Portugal,'" Timmermans shouted, adding later: "Jean-Claude Juncker looked at the plans of Portugal and said 'OK, this can work.' And then Manfred Weber said from the European Parliament 'No, we will not allow this. We should punish Portugal.'"

"That's not true," Weber tried to protest, but Timmermans had clearly won the exchange.

Other zingers by Timmermans were not directed at his conservative rival but merely intended to grab the attention of voters watching the debate, which was sponsored by the European Broadcasting Union and held in the Parliament plenary chambers in Brussels.

When the conversation turned to corporate taxes, Timmermans jabbed at Amazon's virtual assistant: "We should keep asking Alexa: 'Amazon when are you going to start paying taxes?'" And when the topic of Brexit arose, Timmermans quipped, "The U.K. looks like 'Game of Thrones' on steroids."

According to POLITICO projections, based on national polling, a coalition of the Socialists, Greens and the far left would yield a base of about 250 seats in the new parliament — not enough for a majority but more than the 219 seats projected for the EPP and its natural conservative allies. And that would potentially give Timmermans justification to claim the Socialists should get the first shot at leading a majority coalition.

Another 116 seats are predicted to go to far-right populists and pro-Brexit parties, but Weber has pledged not to form any coalition with them.

Even adding in the liberals, who are projected to win 104 seats, would not give either coalition a majority, leading some analysts to conclude that, in the end, the center left and center right will have to reach an accommodation.

Weber, the leader of the EPP group in Parliament, was not only the main target of his rivals, but was also under substantial pressure to use the debate to project a presidential image that might ease some of the doubts about his lack of previous executive experience. For nearly a quarter-century now, national leaders have only chosen Commission presidents who had served in their own ranks as a head of state or government.

On that front, Weber struggled to assert himself as the front-runner, and found himself caught between defending the EPP's track record but also calling for a renewal of the EU, "to open the next chapter." Weber's main messages — that he wants to promote unity and bring the EU closer to voters — came across as earnest but meek, and he offered little in the way of substantive proposals to back up the rhetoric.

He pushed back on Timmermans and the Socialists' call to impose a standardized minimum wage formula across the EU, citing a recent visit to Portugal where he met young voters. "They are not asking about minimum wages," he said. "The young generation are asking for jobs, good paying jobs." he added. "That's why we need a good economic policy to create these jobs."

Jan Zahradil, the nominee of the right-wing European Conservatives and Reformists party, often outflanked Weber to the right, calling for an end to the "outdated scheme of an ever-closer Union" and instead for an "EU which is scaled back, which is flexible, which is decentralized."

"I would like to have a European Commission which respects all its members, regardless of whether they are big or small, or whether they are from the West or from the East," Zahradil said in his opening statement. "I would like a European Commission, which respects national governments and which cooperates with them, which doesn't fight them, which doesn't patronize them, which doesn't lecture them. Simply speaking, I would like to have a European Union which is doing less, better."

For Vestager, the Danish liberal, it was her first appearance in a Europe-wide debate since she agreed to join ALDE's seven-member slate of lead candidates. In the previous major debates, including in Maastricht and in Florence, ALDE was represented by its group leader in Parliament, former Belgian Prime Minister Guy Verhofstadt.

Throughout Wednesday night's debate, Vestager seemed to search out safe ground, and she used her experience as competition commissioner, a position in which she has won substantial public praise, to present herself as a confident, experienced leader. But she did not put forward any dramatic policy proposals, nor did she offer any fuller explanation of the plans by Macron and others to form their new centrist force.

Asked about tax havens, Vestager said there is work still to do in several EU countries, and she won applause when she added, "A tax haven is a place where everyone pays their taxes."

Vestager was perhaps at her strongest when she told Weber that he could not claim credit for the EPP for the Commission's efforts to fight climate change, invoking her fellow commissioners, Miguel Arias Cañete and Violeta Bulč.

"You sort of insist that my colleague Miguel is EPP, but he didn’t make amazing work because he is EPP; he did that because he is part of the Commission," she said, turning to face Weber directly. "My colleague Violeta, she didn’t pave the way to decarbonize transportation because she is Liberal. We work together as a College [of Commissioners] and this is not a party congregation because climate change is so much bigger than any of us.”