Pressure is growing on Senate Republicans to call Lev Parnas, an associate of President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE’s personal lawyer Rudy Giuliani Rudy GiulianiGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Juan Williams: Breaking down the debates Giuliani criticizes NYC leadership: 'They're killing this city' MORE, to testify in the impeachment trial.

Democrats are opening the door to hearing from Parnas as a witness at the impeachment trial after an explosive round of media interviews and new evidence released by House Democrats, which details Parnas’s role in trying to convince the Ukrainian government to investigate former Vice President Joe Biden Joe BidenSenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE.

The revelations, Democrats argue, underscore the need for witnesses and documents — something Republicans have so far resisted.

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Sen. Kamala Harris Kamala HarrisThe Hill's Campaign Report: Trump and Biden vie for Minnesota | Early voting begins in four states | Blue state GOP governors back Susan Collins Kamala Harris: Black Americans have been 'disproportionately harmed' by Trump Biden town hall draws 3.3 million viewers for CNN MORE (Calif.) became the first Senate Democrat to call for Parnas to testify, telling MSNBC that the accusations levied by Parnas “should be pursued and should be reviewed” by the Senate.

“I think he should be brought before us so that we can determine his credibility. There are many ways to judge credibility,” Harris said.

Sen. Ed Markey Edward (Ed) John MarkeyDemocratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy McConnell says Trump nominee to replace Ginsburg will get Senate vote Massachusetts town clerk resigns after delays to primary vote count MORE (D-Mass.) endorsed that effort, saying Parnas should be added to Democrats’ list of impeachment witnesses.

“Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE cannot be allowed to cover up the truth and protect Donald Trump. The Senate must hear directly from John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE, Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE, and Lev Parnas,” Markey tweeted.

Parnas has offered to testify, saying that along with former national security adviser John Bolton he could “fit in all the dots, I think, because I was on the ground there, and he was over here."

“Why aren't they calling me to testify? ... Call me. Ask me what Biden did wrong ... I think they're very afraid of me,” said Parnas, who has pleaded not guilty to campaign finance violations. He is reportedly looking to cooperate with prosecutors in his case.

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Democrats released communications this week detailing Parnas conversations with Giuliani. The documents sparked a round of new questions days before the impeachment trial gets underway in earnest, including about whether Republicans were tracking former Ukraine Ambassador Marie Yovanovitch Marie YovanovitchGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Strzok: Trump behaving like an authoritarian Powell backs Biden at convention as Democrats rip Trump on security MORE.

Parnas, since then, has engaged in a blitz of TV hits where he’s incriminated former Energy Secretary Rick Perry Rick PerryOVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium OVERNIGHT ENERGY: Trump signs major conservation bill into law | Senate votes to confirm Energy's No. 2 official | Trump Jr. expresses opposition to Pebble Mine project Senate votes to confirm Energy's No. 2 official MORE, Giuliani and President Trump.

“He was aware of all of my movements,” he said of Trump. “I wouldn’t do anything without the consent of Rudy Giuliani or the president.”

Sen. Chris Van Hollen Christopher (Chris) Van HollenMid-Atlantic states sue EPA over Chesapeake Bay pollution Trump payroll-tax deferral for federal workers sparks backlash Senators urge administration to make payroll tax deferral optional for federal workers MORE (D-Md.) described his reaction to watching Parnas’s interview with Rachel Maddow Rachel Anne MaddowMichael Cohen: Trump hates Obama because he's everything he 'wants to be' The Hill's 12:30 Report - Presented by Facebook - Trump floats 0M+ in personal spending for reelection bid Feehery: Unconventionally debunking the latest political conventional wisdom MORE as “wow.”

“All I can say is this: Republican senators who refuse to support the calling of fact witnesses and relevant documents should just resign for dereliction of duty under the Constitution,” he said.

The news dump comes amid a bumpy patch for the Trump administration. The Government Accountability Office (GAO) released a report on Friday accusing the White House of breaking the law with the decision to delay the Ukraine aid at the heart of the impeachment effort.

Parnas and Igor Fruman were arrested last year on allegations that they violated campaign finance laws in order to funnel money as part of a straw donor scheme to numerous Republican committees, including a $325,000 contribution in May 2018 to a pro-Trump super PAC called America First Action.

Democratic leadership and House impeachment managers aren’t ruling out trying to call Parnas as a witness. So far they have indicated they want to hear from Bolton, acting White House chief of staff Mick Mulvaney, Mulvaney's senior adviser Robert Blair and Michael Duffey, the associate director of national security at the Office of Management.

“As for Mr. Parnas, it’s something we wouldn't rule out, but we want to see all of the — evidently there are four sets of emails coming out and I'd want to wait to see those,” Senate Minority Leader Charles Schumer Chuck SchumerPelosi orders Capitol flags at half-staff to honor Ginsburg Ginsburg in statement before her death said she wished not to be replaced until next president is sworn in Democrats call for NRA Foundation to be prohibited from receiving donations from federal employees MORE (D-N.Y.) told reporters during a press conference.

Sen. Dick Durbin Richard (Dick) Joseph DurbinMcConnell focuses on confirming judicial nominees with COVID-19 talks stalled Senate Republicans signal openness to working with Biden Top GOP senator calls for Biden to release list of possible Supreme Court picks MORE (D-Ill.), Schumer’s No. 2, added that Parnas’s communications “make it clear that Rudy Giuliani was negotiating directly, trying to negotiate directly with the president of Ukraine, over this question of military aid and the investigation of the Biden family.”

House Intelligence Committee Chairman 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 (D-Calif.) said in a statement that they were reviewing “his interviews and the materials he has provided to evaluate his potential testimony in the Senate trial.”

The White House has sought to distance itself from Parnas's accusations. Trump said that he had never heard of Parnas, arguing that he takes “thousands and thousands of pictures with people.”

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“I don't even know who this man is, other than I guess he attended fundraisers so I take a picture with him,” Trump told reporters.

Vice President Pence and Secretary of State Mike Pompeo Michael (Mike) Richard PompeoHouse panel halts contempt proceedings against Pompeo after documents turned over Outgoing ambassador to China slams Beijing over coronavirus: 'Could have been contained in Wuhan' Hillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers MORE have also both denied knowing Parnas, with Pence calling his accusations “completely false.”

Senate Republicans brushed off the revelations casting doubt on his credibility. If Democrats decided to try to call Parnas they would need four Republican senators to endorse calling him — so far none have.

“Looks kind of like a shady character,” Sen. John Cornyn John CornynBipartisan praise pours in after Ginsburg's death Chamber of Commerce endorses McSally for reelection Airline job cuts loom in battleground states MORE (R-Texas) told reporters.

Senate Judiciary Committee Chairman Lindsey Graham Lindsey Olin GrahamSenate Republicans face tough decision on replacing Ginsburg Democratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy What Senate Republicans have said about election-year Supreme Court vacancies MORE (R-S.C.) added that “I wouldn't trust him as far as I can throw him.”

Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.) noted that while he wasn’t sure if Parnas is credible, his allegations do line up with other testimony from House impeachment inquiry witnesses including Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE, the U.S. ambassador to the European Union.

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“I don't know whether Parnas is credible. What I know is that every criminal conspiracy is unwound by prosecutors by going after the implementers, then ultimately give you information to go after the person who ordered it. So I don’t know if Parnas is credible, but everything he's saying has frankly been confirmed by other witnesses,” Murphy said.

“It is just an open and shut case to me that the president directed this scheme,” he added, “and Parnas’s testimony fits neatly with what we've already heard.”

Rebecca Kheel contributed.