European leaders will gather on Thursday for a summit in the Transylvanian city of Sibiu, the showpiece event of Romania’s six-month presidency of the EU, the first time the country has taken on the role since it joined in 2007.

Despite the fact the UK is still an EU member, Theresa May has agreed to stay away, to give the other 27 leaders the opportunity to discuss the future of Europe without her. But for observers of European politics who look beyond Brexit, there is likely to be another more significant absentee: Liviu Dragnea, the most powerful politician in the summit’s host country.

Dragnea, the leader of Romania’s ruling Social Democratic party (PSD), has become as vexing a figure for many in Brussels as Hungary’s prime minister, Viktor Orbán, or the head of Poland’s ruling Law and Justice party, Jaroslaw Kaczyński, even if he is lesser-known than his more outspoken regional counterparts due to his behind-the-scenes role.

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Dragnea has been convicted of electoral fraud and is thus barred from being prime minister, but few doubt he calls the shots and effectively runs the government. Critics accuse him of being the main reason why Romania’s presidency has proved to be more of an ordeal than a showcase for the country’s government, and has been marred by a spat with Brussels over judicial concerns.

“It could have been a huge opportunity to prove to our European partners that we are really at the same standards, but also to put on the agenda some issues which are very important for Romania,” said Victor Ponta, the former prime minister who resigned after protests sparked by a nightclub fire in 2015. “Instead, it’s embarrassing and a huge missed opportunity.”

Dragnea, 56, rose to prominence through local politics, rising to the top of the PSD, ostensibly a centre-left party which draws on conservative social policies. He is adept at handling internal politics and balancing regional forces, but less skilled when it comes to public appearances or playing the international field, and prefers a role behind the scenes. Critics say his driving goal is more the accumulation of power and wealth than any political values. “His ideology is himself,” said Ponta, who was once close to Dragnea but has since fallen out with him and launched his own political party.

“He is the person doing everything, telling all the ministers, the prime minister [what to do], they are all putty in his hands,” said Monica Macovei, a former Romanian justice minister who set up the anti-corruption directorate (DNA).

Last year, a Romanian court sentenced Dragnea to three and a half years in jail for abuse of office after a corruption trial, a verdict he is currently appealing. There are also allegations that Dragnea, his family and a cabal of friendly businesspeople enriched themselves using an opaque company named Tel Drum, which has bolstered its coffers with money from EU tenders in recent years. Dragnea, who declined an interview request from the Guardian, has previously denied the allegations.

Meanwhile, the government has for some time been trying to pass a controversial amnesty law that would prevent Dragnea and many others from receiving prison terms. To fire up the base, the PSD has become increasingly belligerent in the face of rebukes from abroad, painting the anti-corruption fight as an attack on Romania itself.

The DNA was led from 2013 to 2018 by Laura Codruţa Kövesi, who oversaw the convictions of hundreds of politicians and officials for corruption, including Dragnea’s conviction for vote rigging. She is now one of two leading candidates for the new role of EU public prosecutor.

Romanian authorities responded by having her indicted for corruption herself in March, banning her from talking to the media or leaving the country. The measures increased frustration with Romania among European partners, especially as they came during the country’s EU presidency, and have since been rescinded.

Facebook Twitter Pinterest Romanian authorities are trying to block the former anti-corruption tsar Laura Codruţa Kövesi from becoming EU public prosecutor. Photograph: Vadim Ghirda/AP

Dragnea has gone on the attack, accusing prosecutors under Kövesi of forming a “shadow state” that mirrors Communist-era methods while pretending to be reform-minded. He has called for an amnesty that would help many whom he claims were unjustly convicted, including himself, avoid jail terms.

Those close to Dragnea paint him as being unfairly targeted by political opponents for minor misdemeanours. “He was accused of manipulating the data to bring more people to the vote. In any other democratic country, getting people out to vote is a good thing,” said Șerban Nicolae, the leader of the PSD fraction in the senate.

Nicolae said the graft cases were hypocritical, given the lack of action over corruption in western Europe, and criticised the “so-called Romanian so-called politicians” who had helped tackle corruption in the country, comparing them to historical Romanian politicians who had ruled only with the approval of the Ottoman empire sultan.

“‘I am the ruler of Romania because the sultan decided’ still works in the unconscious minds of some Romanian politicians … If you are truly a Romanian you have to love your people and love your country. When you act against the interests of your country, you have a problem, not the country,” he said.

In Brussels, there is frustration over the direction the country has taken. “We knew perfectly well at the time that Romania and Bulgaria were not ready,” said one source who was involved in the accession process. “The mistake was in hoping that by becoming member states these two countries would automatically align themselves to European standards ... You can pressure a country when it wants to become a member state, but once it is in, the possibility to get reforms is considerably lower. That is a structural failure of our system.”

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The acrimony is mutual. Elena Dumitru, a Romanian journalist who has investigated corruption in the country’s ruling elite, said the PSD has learned from other regional figures that criticising Brussels and branding political opponents unpatriotic can be a useful device to deflect criticism, even in countries like Romania where support for EU membership is high.

“They started to see with Orbán that this rhetoric works. After seeing it work for Hungary and Poland, they have become much more aware that there’s an electoral pull for something like that,” she said.

Even some supporters of the anti-corruption drive concede there may have been cases where boundaries were overstepped. But Cristian Ghinea, of the opposition Save Romania Union party, said the relentless attacks by Dragnea and other officials have led to a perverse situation where convicted criminals paint themselves as innocent victims of a state machine.

“It’s a level of absurdity beyond reason. In a country where there are still thousands of victims of communist terror alive, to compare these corrupt people going to jail with Stalinist terror is simply shameful,” he said.