Former Italian prime minister Matteo Renzi on Friday threatened to sue a onetime campaign aide to President Trump who claimed that Renzi was part of a scheme, allegedly orchestrated by President Barack Obama, to undermine Trump’s candidacy in 2016.

In an interview with a right-wing Italian newspaper, the aide described a series of events — heavy on conspiracy — in which the very origins of the Mueller investigation into Russian interference in the election began because Obama worked to plant a Maltese professor-turned-spy at a university in Rome. The aide, George Papadopoulos, said that “such an operation” could only have happened with Italian government knowledge, and that Renzi cooperated to carry out the “low blow” against Trump.

The accusation against Renzi, who was prime minister from 2014 until 2016, is not supported by evidence.

But it remains relevant, if only because Trump officials and advisers are increasingly pursuing aspects of Papadopoulos’s broader theory: namely, that the Maltese professor was in fact a Western intelligence plant. It was disclosed earlier this week that Attorney General William P. Barr had paid several personal visits to Italy, including one in late September, where he pushed Italians for information on U.S. election interference and its aftermath.

People familiar with the matter say Barr is particularly interested in the role of the professor, Joseph Mifsud, a murky figure whose allegiances have long been debated by the far right, and who has not surfaced publicly in two years.

Democrats say Trump and his lieutenants are trying to discredit the evidence of Russian interference in the 2016 election.

A former Italian government official familiar with the matter said the Italian position is that Mifsud is “not such a relevant person” and that Rome did nothing to interfere with U.S. politics.

Writing on his authorized Facebook page, Renzi, who recently launched a new political party, said fake news was crossing “national borders” and that the “extent of hoaxes should never be underestimated.” He said he would sue Papadopoulos for slander.

Caroline Polisi, a lawyer for Papadopoulos, declined to comment on Renzi’s legal threat.

Papadopoulos pleaded guilty in 2017 to lying to the FBI and was sentenced last year to 14 days in prison. His guilty plea stemmed from lies he told about Mifsud that hindered agents’ ability to effectively question or detain the professor.

It was Mifsud who had allegedly alerted Papadopoulos that the Russians had “dirt” on Trump’s opponent, Hillary Clinton, in the form of thousands of emails. That conversation eventually made its way to U.S. government officials, after Papadopoulos remarked about what he had learned to an Australian diplomat at a London bar. That Australian relayed the information to the United States after Democratic emails began to leak online. That chain of events is what set into motion the probe led by special counsel Robert S. Mueller III.

The Mueller report notes that Mifsud “had connections to Russia” and “maintained various Russian contacts,” including a former employee of the Internet Research Agency, the Russian organization that carried out a social media disinformation campaign in 2016. But Mifsud has told the Italian media he does not work for Russia.

In April, Trump’s personal lawyer, Rudolph W. Giuliani, said on Fox News that Mifsud was a “a counterintelligence operative, either Maltese or Italian,” who took part in what sounded to him like a “counterintelligence trap” against Papadopoulos.

Ellen Nakashima and Rosalind Helderman contributed to this report.