President Donald Trump’s former campaign chairman, Paul Manafort, has hired new lawyers to represent him in the Russia investigation, a spokesman for Manafort said Friday, as FBI special counsel Robert Mueller homes in on his tax records and overseas lobbying work.

“Paul is girding himself for a long legal battle,” the spokesman, Jason Maloni, told Business Insider. “So he is switching to Miller & Chevalier, which is a more specialised firm.”

Manafort switched to Miller and Chevalier — a boutique firm specializing in tax law and complicated financial crimes that had represented him in the past — from WilmerHale, a larger firm that specialises, among other things, in regulatory and government affairs.

Mueller was a partner at WilmerHale before he was appointed to lead the FBI’s Russia investigation in May. Maloni said Mueller’s history there had nothing to do with why Manafort was shifting firms, however.

“If that was the case, Paul would have switched months ago,” Maloni said, pointing to the fact that Mueller was appointed to lead the FBI investigation in May.

Maloni emphasised that WilmerHale was “fantastic,” and “everything a client would have wanted if they were engaging with Congress.”

“But the landscape has shifted,” he said.

The FBI raided Manafort’s northern Virginia home for tax documents and banking records late last month, signalling that Mueller’s investigation had expanded to look at potential money laundering or violations of international tax laws.

Manafort will be represented by Miller & Chevalier’s Kevin Downing, who is a “real rockstar international tax litigator,” Maloni said. Downing will be supported by Richard Hibey, who was Manafort’s longtime lawyer at Miller & Chevalier before he retired in July.

Manafort’s ties to Russia came under scrutiny last August, when The New York Times discovered that a pro-Russian political party in Ukraine designated him $US12.7 million in undisclosed cash payments. Manafort, a longtime Republican operative, had advised the party and its former leader Viktor Yanukovych for nearly a decade.

Manafort has been associated with at least 15 bank accounts and 10 companies in Cyprus, dating back to 2007, NBC reported in March, and the FBI has now issued grand jury subpoenas to several banks for Manafort’s records, according to Bloomberg.

Manafort also attended a meeting last year at Trump Tower with Trump’s son Donald Trump Jr., son-in-law Jared Kushner, and two Russian lobbyists who were said to have offered dirt on Hillary Clinton.

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