Sen. Richard Blumenthal (D-Conn.) is urging the chairman of the Senate Judiciary Committee to subpoena Donald Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE Jr. to testify publicly before the panel.

The Democratic senator, a member of the committee, sent a letter to Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyCollins says she will vote 'no' on Supreme Court nominee before election The Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Gardner signals support for taking up Supreme Court nominee this year MORE (R-Iowa) on Tuesday asking him to “immediately issue a subpoena for public testimony and documents from Donald Trump, Jr.”

“Recent revelations have shown beyond question that the American people can only feel certain that Mr. Trump, Jr. has been fully forthcoming if he is subject to a subpoena,” Blumenthal wrote.

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He added that the Senate Judiciary Committee should “issue a subpoena to compel him to fully account for his actions in front of the American people and to provide this committee with the documents we need to fulfill our important oversight responsibilities.”

Under Judiciary Committee rules, the panel can only issue a subpoena with the support of a majority of the committee’s members or when Grassley and Sen. Dianne Feinstein Dianne Emiel FeinsteinBiden leads Trump by 12 points among Catholic voters: poll Names to watch as Trump picks Ginsburg replacement on Supreme Court McConnell says Trump nominee to replace Ginsburg will get Senate vote MORE (D-Calif.), the ranking member, are in agreement.

Trump Jr. is expected to appear before the House Intelligence Committee on Wednesday, and has agreed to sit down with staff from the Senate Intelligence Committee. Both panels are investigating Russia’s interference in the 2016 presidential campaign.

Trump Jr. confirmed last month that he exchanged messages on Twitter with WikiLeaks during his father’s campaign. The website published troves of leaked Democratic emails believed to have been stolen by Russian-backed hackers.

Blumenthal pointed to the revelation as one of a “number of cascading disclosures that suggest collusion between the Trump campaign and Russian officials.”

“Mr. Trump, Jr.’s refusal to testify before the Committee means that key questions have been left unanswered,” he said.

The Judiciary Committee — which is conducting its own investigation into the 2016 election and FBI Director James Comey’s firing — initially issued a subpoena earlier this year, but then backed off saying Trump Jr.'s attorneys had agreed to cooperate.

Trump Jr. met with Judiciary Committee staff in September and discussed a July 2016 meeting, which he took part in, involving a Russian lawyer promising dirt on Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE.

But Democrats on the committee have been clamoring for him to testify publicly, and Grassley defended the closed-door meeting by saying that Trump Jr. would also testify publicly.