Retired CIA operations officer Stephen Hall, who was the Station Chief at the Embassy of the United States in Moscow, penned an op-ed for the Washington Post on Friday explaining why former Donald Trump campaign chairman Paul Manafort would have been “a prime target” for Russian intelligence officials working on behalf of the Kremlin.

Hall pointed to recent reports that, in an email exchange, Manafort offered Russian oligarch Oleg Deripaska “private briefings” on the status of the campaign less than two weeks before Trump clutched the Republican nomination.

As Hall noted, Deripaska is “among the 2-3 oligarchs Putin turns to on a regular basis,” a fact Manafort would have understood “clearly, of course,” given his career as an influence broker prior to joining the Trump campaign.

“If you choose to wade in that swamp, and you are trying to make money doing it, you cannot help becoming highly attuned to the power relationships in that part of the world,” Hall wrote.

Manafort spokesman Jason Maloni described Manafort’s offer as an “innocuous” attempt to collect past debts, telling the Post, “It’s no secret Mr. Manafort was owed money by past clients.”

But Manafort was also indebted to Russian interests, according to records from Cyprus—a noted financial tax haven. In fact, Deripaska filed a complaint in a Virginia court in 2015 alleging Manafort and his partners owed him $19 million, the New York Times reports.

In considering what Hall described as the “ideal spy” for Russian intelligence services, the former CIA intelligence officer argued Manafort would be “irresistible to Russian intelligence services.”

“In the world of Russian human intelligence collection, the ideal spy looks something like this: an individual with a significant financial vulnerability or motivation (such as debt or a threat of meaningful financial loss); someone with access to inside information of interest to the Russian government; a person who understands the need for discretion and, if necessary, secrecy,” Hall explained.

“Any Russian intelligence officer worth his salt would have identified Manafort as meeting all those qualification,” he added.