FLORENCE, Italy — Candidates representing the four leading pro-EU political families in the race for the European Commission's top job battled it out in a debate Thursday night that was so contentious at times, it was hard to remember they could well end up as coalition allies after this month's European election.

The candidates — Manfred Weber of the center-right European People's Party (EPP), Frans Timmermans of the Party of European Socialists (PES), Guy Verhofstadt of the Alliance of Liberals and Democrats for Europe (ALDE) and Ska Keller of the European Green Party — offered contrasting views of the future of the EU, especially on social and economic policies. Some of the sharpest clashes came over security policy and whether the bloc should aspire to build an EU army.

But they found common ground in complaining that EU countries were impeding integration in many policy areas.

Set on the sprawling Villa Salviati estate on the outskirts of Florence, a repository for the EU's archives, the debate also marked the first time three leading voices in the race — Weber, Timmermans and Verhofstadt — were on stage together. At a debate earlier this week in Maastricht in the Netherlands, Weber was a no-show.

Weber and Timmermans, representing the parties that traditionally win the most seats in Parliament, have the most to gain from preserving the Spitzenkandidat system.

Far-right nationalist forces, which are projected to win their largest number of seats in modern EU history, were not represented at the debate, organized by the European University Institute and moderated by Martin Sandbu of the Financial Times.

Here are four takeaways from the lead candidates' evening under the Tuscan sun.

The new center

Verhofstadt used his opening statement to declare publicly that ALDE plans to dissolve after this month's election and form a new, centrist political family in partnership with French President Emmanuel Macron and candidates on his "Renaissance" list.

Verhofstadt also defended ALDE's decision not to put forward a single candidate but to field a slate of seven nominees, saying it was a way to protest the EU's Spitzenkandidat process, whereby the lead candidate of the political group that wins the most seats in the European election becomes Commission president. He also said ALDE's plans were meant to protest the refusal of other families to support the idea of transnational candidate lists.

"We are going to create a new group, a global group, a pro-European centrist group, together with Emmanuel Macron," Verhofstadt said.

"People cannot directly elect the Spitzenkandidat," he said. "Most of you cannot vote for the candidates here on this stage. That's the reason. We say 'yes' to a Spitzenkandidaten system if people can vote for it, if we have transnational lists."

While Verhofstadt accused Weber and the EPP of breaking a deal to create transnational lists for this year's election, Weber and Timmermans pummeled Verhofstadt for flip-flopping on the lead candidate process. Timmermans even seized on a Brexit question to say that if Verhofstadt could change his mind on the lead candidate, then Britain should be allowed to change its mind and stay in the EU.

The fight reflects how Weber and Timmermans, representing the parties that traditionally win the most seats in Parliament, have the most to gain from preserving a system that expects the heads of state and government on the European Council to nominate as Commission president the lead candidate of the party winning the most seats — even though the Council has said it will not be bound to the system.

It's no picnic being a front-runner

As the nominee of the EPP, which is projected to once again win the most seats in Parliament, Weber is widely regarded as the front-runner for the Commission's top job. That means he was both the primary target for all the other candidates, and faced greater pressure to appear presidential.

Weber came under assault relatively quickly. First, his opponents used the opening topic of migration to portray him as close to Hungarian Prime Minister Viktor Orbán. Then, the three candidates used a question about economic policy to paint Weber, a German member of the European Parliament, as synonymous with austerity initiatives. As Weber spoke of the success of the EPP-led initiatives, the others stood by smirking.

"From our point of view, what we have seen in recent years inside the European Union is indeed a very harsh austerity program, which has not been leading to growth and development at all," Keller said. She accused Weber of offering to ease the austerity push only because he wants to become Commission president.

Some of the sharpest clashes between the candidates were on the question of whether the EU should aspire to develop an army.

But while Weber sought to portray EPP stewardship of the EU as a success, he struggled to project the gravitas of an aspiring world leader. Verhofstadt, a former Belgian prime minister, and Timmermans, a former Dutch foreign minister now serving as first vice president of the Commission, each came across as more confident and forceful.

Weber spoke repeatedly about a few core proposals of his campaign, including "a master plan against cancer" and creating an "FBI at a European level." But often he fell back on platitudes. "I believe in innovation," he said in response to a question on climate change.

Timmermans did not offer much more in the way of concrete proposals but he sounded like a veteran official with experience of tough issues. "If we screw this up, none of us in this room can look our children in the eye anymore," he said. "I know it’s going to be painful and we need to be honest about the fact that this transition is going to be painful. But we need to make it. Otherwise the problems we will be facing will be out of control. And we can make it. We can have ecological and economic transformation into a sustainable world."

Fight, fight, fight (over an EU army)

Some of the sharpest clashes between the candidates were on the question of whether the EU should aspire to develop an army — with Verhofstadt and Weber generally in favor, and Timmermans and Keller expressing skepticism if not outright opposition.

"European army!" Verhofstadt declared after expressing his agreement with Weber that there should be an EU version of the FBI.

"The biggest waste of money in the European Union is the military, the way we organize it," Verhostadt said. "We spend nearly half of the Americans. We spend three times more than the Russians on military in Europe, but I am not sure if the Russians come this way that we are capable to stop them. A European army of 20,000 people in 2024. Let’s do it."

Timmermans disagreed with the FBI proposal, and was especially dismissive of talk of an EU army. "Don’t overpromise," he said. "There is not going to be a European army anytime soon."

Weber jumped in on Verhofstadt's side. "We should have great ambitions," he said, adding: "It’s a fundamental idea to never have war again in Europe. It's today unthinkable but with a common European army it would be totally unthinkable."

Bottom line: No matter who becomes Commission president, the EU will continue to struggle on defense and foreign policy.

Pro-EU — but what exactly is the EU, again?

The candidates' closing statements helped sum up just how differently they view the EU and its future.

Verhofstadt insisted Europe must unite further to compete against China, India and the U.S.

"The new world order is not an order of nation states," he said. "The new world order is an order of empires — empires like China, like India, like Russia, like the United States of America." He added, "Only together in a real European Union, we can succeed and survive."

Weber focused on his general campaign theme about needing to bring the EU closer to European citizens, as the best way to answer populist and nationalist rhetoric.

Keller urged voters to think about the future of the planet and about younger generations, who have taken to the streets to protest climate change.

"The essence of Europe — let’s keep it alive," he said "The essence of Europe is compromise, the readiness to sit together and find a common understanding for the future and to do so I think we need optimism. We can be proud of what we achieved but we can go further."

He said many citizens still needed to be convinced to believe in the EU. "In the EPP we want to show people this Europe is not a distant Europe," he said. "It’s my Europe. Europe can feel like being at home."

Timmermans warned that the EU is fighting for survival.

"I believe this is the first time since the beginning of European integration, that this European Union could actually break apart," he said, adding: "We as politicians have a task to give a voice to the people who now are silent to stand up for what they believe in, to give them courage, by being courageous ourselves, and address the populists, address the right extreme, say that we don't want a society based on confrontation and hate and exclusion."

And Keller urged voters to think about the future of the planet and about younger generations, who have taken to the streets to protest climate change.

"There's actually a group of people who won't be able to choose their future and that's young people who haven't reached yet the voting age," Keller said. "But I think it's especially their future that we should be looking into because any decision we are taking now will be affecting mostly young people."

She added, "So let's go to vote taking into account the future of the children, of the grandchildren."