WASHINGTON – Democrats on a House committee are pressuring the White House to release a wide array of documents about the security clearances granted to former National Security Adviser Michael Flynn and Jared Kushner, President Donald Trump‘s son-in-law and top aide.

In a letter Wednesday, 18 members of the House Oversight and Government Reform Committee said they have “serious concerns” about how the White House is handling classified information and who is being allowed access to such sensitive material. The letter, citing press reports, singles out Kushner for failing to disclose numerous contacts with foreign officials on his security clearance questionnaire. It also questions why the White House allowed Flynn to have access to classified information after learning that he had misled administration officials about the content of conversations with a Russian diplomat.

Josh Raffel, a White House spokesman for Kushner, did not immediately comment on the letter. Kushner’s attorney, Jamie Gorelick, said she hadn’t seen the letter and was out of the country. Flynn’s attorney, Robert Kelner, declined to comment.

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Flynn, who was later fired over the misleading statements, is currently the subject of congressional probes and the investigation led by special counsel Robert Mueller into Russia’s interference in the 2016 presidential election and possible collusion with Trump associates.

Kushner, who is currently in the Middle East attempting to broker a peace deal between the Israeli and Palestinian leaders, has said through his lawyers that he is willing to talk to federal and congressional investigators about his foreign contacts and his work on the Trump campaign.

Gorelick has previously acknowledged that Kushner failed to disclose some of his contacts with Russian government officials while he was filling out his security clearance questionnaire. Gorelick said in April that the omissions were an “administrative error,” adding that “there was no intent to obscure any foreign meetings, including those with Russia.”

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Among those meetings that he omitted was a December meeting with Sergey Kislyak, Russia’s ambassador to the U.S., and another with the head of a Russian bank.

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During the Kislyak meeting, which took place at Trump Tower in New York last December, Kushner proposed a secret back channel between the Kremlin and the Trump transition team, according to a person familiar with the discussions.

In his talks with Kislyak, Kushner broached the idea of a line of communication with Russia to promote sensitive discussions exploring the new administration’s possible options in Syria. The goal, according to the person familiar with the meeting, was to connect Flynn, who was Trump’s top national security aide at the time, with Russian military leaders. The Washington Post, which first reported the session, said Flynn also attended the meeting.

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Kushner also separately met during the transition period with Sergey Gorkov, the top executive of Russia’s state-supported VEB bank. The White House said Kushner was acting in his capacity as a transition official at the time. The bank has said that the meeting was part of a new investment strategy that was being unveiled to leading world financial institutions as well as “the head of the Kushner Companies.”

In their letter, the Democrats on the oversight committee request that the White House provide any documents or communications regarding these meetings or other contacts Kushner had with Russian government officials and businesses as well as any documents or communications detailing the classified information that Kushner and Flynn had access to since December.

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They also request documents related to any White House official who has been granted access to classified information while under investigation by law enforcement and any White House official who resigned or was terminated due to a criminal investigation or an inability to obtain a security clearance.

The Democrats’ letter was copied to the committee’s newly installed Republican chairman, Rep. Trey Gowdy of South Carolina. But it’s unclear if the letter will have much success in prying loose documents from the White House. So far, the Trump administration has largely ignored requests for documents from Democratic lawmakers, only turning over documents when Republicans join in the request.