Where Paul Manafort goes, smoke seems to follow. His three-month run as Donald Trump’s presidential campaign chairman ended shortly after The New York Times suggested that Manafort may have received $12.7 million in dubious payments from a pro-Russian Ukrainian political party. (Ukrainian prosecutors later announced that they had found no evidence of such payments.) There were also the 15 accounts in Cyprus banks that Manafort shuttered in 2012. Over the weekend, The Times reported that Manafort had attended the now infamous meeting with a Russian attorney, along with Donald Trump Jr. and Jared Kushner, seeking damaging information on Hillary Clinton just after Trump had clinched the G.O.P. nomination last May.

Now Robert Mueller is trying to determine whether there is an actual underlying fire creating the Manafort haze. The special counsel, along with state and city prosecutors in New York, want to know if the money trail leads back to Russian banks, including Vnesheconombank (VNB), the state-owned financial institution whose chief executive met with Kushner last fall. Banks can be instruments of modern Russian espionage tradecraft, entangling targets, realigning their interests with those of Russia, even without their knowledge. It’s these patterns that investigators are trying to trace.

Jason Maloni, a spokesman for Manafort, says that his client’s representatives believe he complied with applicable laws, and that the decision to close the Cypriot accounts was made because of the collapse of the country’s banking system. Manafort, who has openly acknowledged working with Russian oligarch Oleg Deripaska on commercial projects long pre-dating the Trump campaign, has said, “I did not work for the Russian government.”

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Manafort has a long history with big money, high-risk clients. In the 80s he was hired to help Philippine despot Ferdinand Marcos hold onto power. Manafort also lobbied on behalf of brutal Angolan rebel leader Jonas Savimbi, and in service of Zaire’s repressive Mobutu Sese Seko. In a hacked text allegedly sent by one of Manafort’s own daughters, who happens to be a lawyer, some of the wealth that he has accumulated was characterized as “blood money.”

Closer to home is a series of New York real-estate deals in which Manafort, or limited liability companies with which he was involved, bought properties for cash and then took out large mortgages. Manafort has said that his “personal investments in real-estate are all ordinary business transactions.” And perhaps that’s all true, and thoroughly benign. The political questions swirling around his activities would nevertheless linger. Were people trying to buy something through Manafort, a prosecution source asks, either in the presidential election or in Trump foreign policy? That’s part of the reason behind Mueller’s two most recent staff hires: Andrew Goldstein, who headed the Souther District of New York’s public corruption unit under U.S. Attorney Preet Bharara, and Zainab Ahmad, who prosecuted 13 terrorism cases without a defeat as an assistant U.S. attorney in New York’s Eastern District. Goldstein and Ahmad are deeply experienced in piecing together complex webs of money and influence.