The Washington Post reported Friday "the senior White House adviser under scrutiny by investigators is someone close to the president." Law enforcement officials would not further identify the individual.
Several former Trump associates, including former campaign chairman Paul Manafort and former national security adviser Michael Flynn, are under investigation by the bureau with regard to their foreign contacts and payments throughout 2016.
Trump's son-in-law and senior adviser, Jared Kushner, has also landed on investigators' radar for meeting privately with Sergey Gorkov, the CEO of a state-owned Russian bank, during the transition period.
Kushner also met with Russia's ambassador to the US, Sergey Kislyak, in December at Trump Tower with Flynn. Kislyak set up the meeting between Kushner and Gorkov, according to a previous report from The Times. Attorney General Jeff Sessions has also come under scrutiny for meeting with Kislyak during last year's campaign, something he did not disclose during his confirmation hearings.
Deputy Attorney General Rod Rosenstein appointed a special counsel to lead the FBI's probe into the Russia investigation earlier this week, two days after The Times reported that Trump had pressured former FBI Director James Comey to drop the bureau's probe into Flynn.
The Times reported Friday that during their meeting in the Oval Office last week, Trump told Russian diplomats that Comey — whom Trump fired the day before meeting with the Russians — was "a nut job."
"I just fired the head of the FBI ... a real nut job," Trump said, according to an official summary of the meeting read to the New York Times by a US official. "I faced great pressure because of Russia. That’s taken off."