Rep. Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE (Calif.), the ranking Democrat on the House Intelligence Committee, is upping the pressure on Chairman Devin Nunes (R-Calif.) to move forward with the panel's investigation into Russian meddling in the U.S. presidential election.

In a tweet Wednesday morning, Schiff asked what "the holdup" was for hearing testimony from former acting Attorney General Sally Yates, former director of national security James Clapper and former CIA Director John Brennan.

Sally Yates is willing to testify, WH says they want her to testify, public wants to hear from her, Brennan and Clapper...what's the holdup? — Adam Schiff (@RepAdamSchiff) March 29, 2017

Nunes raised eyebrows when he canceled a hearing on Russia where Yates was to testify the same day the Trump administration reportedly voiced objections to him about her planned testimony.

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Yates briefly led the Justice Department while Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE moved through Senate confirmation. She was fired by Trump after she refused to defend in court his executive order temporarily barring refugees and travelers from a handful of predominately Muslim countries.

After she was fired, it was revealed that Yates had notified the White House that then-national security adviser Michael Flynn had not properly explained his contact with Russia's ambassador to the U.S., according to a report published Tuesday in The Washington Post.

The incident led to Flynn's resignation. The Post referenced documents that showed the Justice Department told Yates her testimony would have to be seriously limited because of executive privilege, which protects executive branch documents and information from having to be turned over in certain cases.

According to the series of letters, a Justice Department official told Yates's lawyer, David O'Neill, that she would need “consent” from the White House in order to discuss her conversations with the White House.

White House press secretary Sean Spicer on Tuesday blasted the Post report, denying that President Trump blocked Yates from testifying.

"I hope she testifies," Spicer said. "I look forward to it. ... If they choose to move forward, great. We have no problem with her testifying, plain and simple. The report in The Washington Post is 100 percent false."

Tuesday afternoon, Rep. Walter Jones (N.C.) became the first Republican to join Democrats in calling for Nunes to hand over control of the Russian probe, saying he's lost credibility.