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Rick Gates, a campaign adviser to President Trump and former business partner of Paul Manafort, is close to finalizing a plea deal with Special Counsel Robert Mueller's office, several people with knowledge of the matter told CNN Thursday.

This would make Gates the third person known to be cooperating with Mueller in his investigation into Russian meddling in the 2016 presidential election, along with Michael Flynn and George Papadopoulos. Gates has been in negotiations with Mueller's team for about a month, CNN reports, and he's had what lawyers call a "Queen for a Day" interview, which involves a defendant answering questions from prosecutors about their own case and other potential criminal activity. After interviews like this, prosecutors investigate the information they received, then negotiate charges and potential sentences. Gates' plea deal could be announced in the next few days, CNN reports.

In October, Gates and Manafort, Trump's former campaign chairman, pleaded not guilty to charges of money laundering and failure to disclose financial assets. If Gates flipped, it would put pressure on Manafort, and people close to the case told CNN that investigators are preparing to file new tax-related charges against Gates, as well as charges against Manafort on work he did before joining the Trump campaign.