An investigation into alleged corruption by the former prime minister of Spain, José Luis Rodríguez Zapatero, threatens not only to taint his legacy but to bring about the collapse of the left-wing government.Last week, a national court investigating judge named Zapatero as being formally under investigation, accusing the former Socialist Party leader of being at the centre of a “stable and hierarchical structure of influence peddling” which had used his name and image to secure a €53-million government bailout for Plus Ultra airline after the pandemic. Zapatero had received substantial commissions for this operation, according to the allegations, with about €250,000 being funnelled into a company owned by his two daughters. The judge also alleged that the network operated internationally, benefiting from transactions in gold, shares and oil, with particularly close links to Venezuela.His associate, Julio Martínez, was arrested in December in connection with the case.Zapatero (65) led the country between 2004 and 2011. This is the first time that a former prime minister has faced a criminal investigation.In a video posted online shortly after the news broke and his offices were searched by police, Zapatero denied any wrongdoing.“I want to make abundantly clear that I have never carried out any transaction in association with Plus Ultra with any public entity or in the public sector, nor have I done so with any other entity,” he said.On the political left, Zapatero is highly regarded, with his government introducing same-sex marriage and securing the end of a four-decade campaign of violence by Basque separatist group Eta.He has become a trusted ally of Socialist prime minister Pedro Sánchez. In 2023, Zapatero’s campaigning ahead of a general election was seen as key in helping keep Sánchez in power. More recently, he has been deployed to manage the Socialists’ parliamentary relationship with Catalan nationalists.Sánchez has publicly defended his innocence, offering “all my support” to his predecessor, with his Socialist ministers expressing similar sentiment. [ Tens of thousands march in Madrid to demand Spanish prime minister resignsOpens in new window ]However, this is only the latest in a series of judicial cases which have been accumulating around Sánchez and his allies in recent months. The prime minister’s own brother, David, is due to go on trial this week for influence peddling and a judge has been investigating the business affairs of Sánchez’s wife, Begoña Gómez, for more than two years.The government has treated those cases as politically motivated, pointing to what it sees as the unusual zeal of investigators.However, Sánchez has had to acknowledge his own misjudgment after two former close allies and high-ranking Socialist officials, José Luis Ábalos and Santos Cerdán, were accused of running a massive kickback scheme. Ábalos is awaiting the verdict of his recent trial.So far, Sánchez has resisted the opposition’s calls for him to resign or call elections as these cases have mounted. But the Zapatero probe, which was announced two days after the Socialists suffered a heavy defeat in a regional election in Andalucía, is seen as a potential tipping point. With his minority government relying on an array of parliamentary partners it is they, more than the right-wing opposition, which could decide whether this scandal brings down the administration.Although several parties on the left initially expressed disbelief at the news of the investigation, some even suggesting it may be a conspiracy, support for Zapatero has become less vocal as more evidence from the case has come to light. The junior partner in the governing coalition, Sumar, has been cautious, calling for an explanation from the former prime minister.The far-left Podemos, meanwhile, has been more outspoken, with party leader Ione Belarra warning that the case “looks ugly”.“The future of Zapatero is completely tied to the future of the government and the prime minister,” she said.