A Russian businessman who was an unwitting source for the so-called Steele dossier developed a relationship with Trump campaign aide George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE in 2016, The Washington Post reported Thursday.

According to the newspaper, Sergei Millian spent months establishing a relationship with Papadopoulos and offered him a consulting contract to work for an unidentified Russian at the same time he was working for then-presidential candidate Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE. Papadopoulos said he turned down the offer.

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The Post noted that the extent of Millian's involvement in Trump's orbit remains unclear, but that his ties to Papadopoulos were not previously known.

Millian previously claimed in a 2016 interview that he met with former Trump lawyer Michael Cohen and signed a deal to sell Trump-branded real estate units in Florida. Cohen has denied those assertions, calling Millian a fraud with no legitimate connection to Trump, the Post reported.

The businessman was previously reported to have been one of the sources for the Steele dossier, which was compiled by former British intelligence agent Christopher Steele and contains salacious allegations about Trump's ties to Moscow. Some of the claims remain unverified.

Also in 2016, Millian offered to serve as a go-between for a Belarusian author with ties to the Russian government and the Trump campaign, the Post reported. The author, Mikhahil Morgulis, said he never heard from the campaign.

The Post reported that the Senate and House intelligence committees have each unsuccessfully tried to interview Millian.

Millian is one of several elusive figures to emerge from the investigations into Russian interference in the 2016 election. Trump has denied that he colluded with Russia during the campaign, and has derided the Steele dossier as "phony."

House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffChris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Trump casts doubt on Ginsburg statement, wonders if it was written by Schiff, Pelosi or Schumer Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-Calif.) said Wednesday that he would launch a probe that extends beyond potential links between the Trump campaign and Russia that would investigate whether Trump's decisions as president have been motivated by financial gain.

Papadopoulos, a former campaign adviser whom Trump has described as a low-level staffer, is one of several previous associates of the president to either plead guilty or be indicted by special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE.

He served 12 days in prison in September after pleading guilty to lying to FBI agents about his contacts with Russia-linked individuals.