Donald Trump Jr. is expected to meet with congressional investigators on Thursday for talks about the Trump campaign's contacts with Russians during the 2016 presidential race, two committee sources said.

Specifically, the Senate Judiciary Committee is likely to use the closed-door interview to grill Trump Jr. on his meeting in June 2016 with a Russian contingent that was described as offering dirt on his father's rival, Hillary Clinton.

President Trump's son-in-law Jared Kushner and then-campaign chairman Paul Manafort also attended the meeting at Trump Tower.

Trump Jr. released a thread of emails this summer that depicted an outreach that began with Russia's top federal prosecutor in Moscow. That official met with a billionaire business friend of Trump's, who called his son, who called his publicist, who pitched Trump Jr. on a Russian offer of "high level" and "sensitive" information damaging to Clinton.

Trump Jr. had initially said that the meeting focused on Russian adoptions and that the campaign ultimately did not receive damaging information on Clinton. The White House has acknowledged that President Trump had a hand in drafting that initial explanation Trump Jr. gave.

"Adoptions" is understood to be a term of art that refers to sanctions imposed by Congress in 2012 on a small group of elite Russians. President Vladimir Putin reacted angrily by banning the adoption of Russian children by Americans, and lobbyists have been working inside the U.S. ever since to get Congress to overturn the financial restrictions.

The Russians who met with Trump Jr. are longtime workers on behalf of overturning the sanctions.

The New York City meeting they had with the Trump campaign has emerged as an important point of the investigations into potential collusion between the Trump campaign and Russia's attack on the 2016 election. The Senate Intelligence Committee and its House counterpart are both conducting inquiries into Russia's interference in the 2016 election, while special counsel Robert Mueller is overseeing the FBI's probe.

The Senate Judiciary Committee is not the primary venue on Capitol Hill to dig into the Russian imbroglio, but it nonetheless has ramped up its investigative efforts as well. Committee staff members met last month with Glenn Simpson, the co-founder of the strategic research firm that commissioned the unsubstantiated dossier that claims Trump conspired with Russia to win the election.

Trump has denied the allegations.

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