Mar-a-Lago – the Palm Beach resort and residence where Donald Trump reportedly stored nuclear secrets among a trove of highly classified documents for 18 months since leaving the White House – is a magnet for foreign spies, former intelligence officials have warned.

The Washington Post reported that a document describing an unspecified foreign government’s defences, including its nuclear capabilities, was one of the many highly secret papers Trump took away from the White House when he left office in January 2021.

There were also documents marked SAP, for Special-Access Programmes, which are often about US intelligence operations and whose circulation is severely restricted, even among administration officials with top security clearance.

Potentially most disturbing of all, there were papers stamped HCS, Humint Control Systems, involving human intelligence gathered from agents in enemy countries, whose lives would be in danger if their identities were compromised.

The Office of the Director of National Intelligence is conducting a damage assessment review which is focused on the sensitivity of the documents, but US officials said it is the job of FBI counter-intelligence to assess who may have gained access to them.

That is a wide field. The home of a former president with a history of being enthralled by foreign autocrats, distrustful of US security services, and boastful about his knowledge of secrets, is an obvious foreign intelligence target.

“I know that national security professionals inside government, my former colleagues, [they] are shaking their heads at what damage might have been done,” John Brennan, former CIA director, told MSNBC.

“I’m sure Mar-a-Lago was being targeted by Russian intelligence and other intelligence services over the course of the last 18 or 20 months, and if they were able to get individuals into that facility, and access those rooms where those documents were and made copies of those documents, that’s what they would do.”

Last month, the Organised Crime and Corruption Reporting Project reported that a Russian-speaking immigrant from Ukraine was able to mingle with the former president’s family and friends at Mar-a-Lago, posing as Anna de Rothschild, presenting herself as being an heiress of the banking dynasty.

Inna Yashchyshyn, the daughter of a truck driver who emigrated to Canada, regaled those around her with tales of vineyards and estates and growing up in Monaco, and even met the former president in person, getting herself photographed with him on a golfing green.

There is no evidence that Yashchyshyn was a spy, but the episode underlined how easy it is to get into Mar-a-Lago. During Trump’s presidency, two Chinese women were caught trespassing there on separate occasions.

One of them, Yujing Zhang, was in possession of four mobile phones, a laptop, an external hard drive, and a thumb drive later found to carry malware. In her hotel room, investigators found nine USB drives, five SIM cards and a “signal detector” device for spotting hidden microphones or cameras. She was found guilty of unlawfully entering a restricted building and making false statements to a federal officer, and deported to China in 2021.

The guests, invited or otherwise, are not the only security concern. In 2021, the Trump Organization sought 87 foreign workers for positions at Mar-a-Lago, with wages starting at $11.96 an hour.

“Any competent foreign intelligence service, whether those belonging to China, those belonging to Iran, to Cuba, certainly including Russia are … and were interested in gaining access to Mar-a-Lago,” Peter Strzok, former deputy assistant director of counter-intelligence at the FBI, told MSNBC.