Special counsel Robert Mueller is looking into possible money laundering by President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE's former campaign chairman, Paul Manafort, as part of his investigation into Russia's interference in the 2016 presidential election, The Wall Street Journal reported Thursday.

It's not the first time Manafort's dealings have come under scrutiny. New York Attorney General Eric Schneiderman (D) and Manhattan District Attorney Cyrus Vance Jr. are also looking into Manafort's real estate transactions for possible money laundering and fraud.

Mueller's investigation is focusing on Russian efforts to meddle in the 2016 election, as well as possible collusion between the Trump campaign and Moscow.

The special counsel investigation is also looking into possible financial ties between members of the Trump campaign and Russian interests.

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Mueller's review of Manafort's financial transactions has been in the works for several weeks, according to the Journal.

The Senate and House Intelligence committees are also looking into Manafort's financial dealings as part of their investigations into Russian election meddling.

On Wednesday, The New York Times reported that Manafort owed as much as $17 million in debt to pro-Russia interests before signing on as Trump's campaign manager in March 2016. Manafort worked for Trump's campaign for free.

Manafort and Trump's eldest son, Donald Trump Jr., have been called to testify before the Senate Judiciary Committee next week as part of that panel's own Russia investigation. The Senate Judiciary Committee is threatening to subpoena them if they do not come voluntarily.