Newly declassified FBI documents show that the bureau discovered former US congressman Eric Swalwell’s relationship with Christine Fang while investigating whether the suspected Chinese intelligence operative could be recruited as a double agent. The files, released on Monday by the White House Government Transparency Task Force, detail the FBI’s efforts to assess Fang, also known as Fang Fang, and her contacts with US politicians.

A 2013 FBI memo says Swalwell joked that Fang was suspected of being associated with China’s Ministry of State Security (MSS), which it described as the equivalent of the Chinese CIA.

“Congressman Eric SWALWELL… commented that [Fang] was suspected as associated with the ‘Chinese CIA’ [MSS], albeit in a joking manner,” the memo said. Fang, the document added, joked that MSS officers were “either old men or ladies” and therefore she could not be one of them.

The FBI had codenamed Fang “Rusty Thumbs” and explored recruiting her through an undercover operation. Investigators were aware that her parents were Chinese intelligence officers and that she had personal “affiliations” with China’s spy agency, according to the files. The documents say Fang told agents she could “use her sexuality on politicians” because she was “young and pretty”. Investigators assessed that her motivations appeared to be centred on “money and power” and noted what they described as “certain egotistical/narcissistic traits”.

The FBI ultimately concluded in March 2014 that Fang could not be trusted to reliably provide information on China in exchange for money and closed the recruitment effort.

Six days later, the bureau opened an investigation into Swalwell and Fang’s access to him.

Swalwell later told investigators that he had had “physical relations with Fang on a handful of occasions”. According to the documents, the relationship continued even after Swalwell had entered Congress.

The FBI gave Swalwell a classified briefing about Fang on 30 April 2015. At the time, the documents say, he was seeing her roughly every two months. The relationship raised particular concerns because Swalwell was serving on the House Permanent Select Committee on Intelligence, which oversees US intelligence agencies.

Swalwell has previously said he ended contact with Fang and co-operated with the FBI investigation. His attorneys have said he was never accused of wrongdoing in connection with the matter.

The documents had been marked declassified in March but were not publicly released until Monday. Swalwell had previously threatened legal action to prevent the FBI from releasing the files, arguing that their publication was an attempt to damage his campaign for California governor.

His attorneys said in a cease-and-desist letter that “the Congressman has never been accused of wrongdoing in that matter” and described the planned release as an attempt to “smear him and undermine his campaign”.

Swalwell’s ties to Fang were first publicly reported in 2020. Fang, who has since left the US and has reportedly been barred from returning, was suspected of cultivating relationships with politicians and other influential figures in California.

Swalwell left Congress in April after facing allegations of sexual misconduct and rape from former staff members, which he has denied.