House Republicans are intensifying a multipronged assault to chip away at special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s investigation into Russian interference in the U.S. election.

A vocal group of conservative members has for weeks blitzed the airwaves decrying bias in Mueller’s investigation and on Thursday, two prominent members called for 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 to step down from the Department of Justice (DOJ) — a resignation that could clear the way for the special counsel’s dismissal.

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On Wednesday, the chairman of the House Intelligence Committee, Devin Nunes Devin Gerald NunesSunday shows preview: With less than two months to go, race for the White House heats up Sunday shows preview: Republicans gear up for national convention, USPS debate continues in Washington Sunday shows preview: White House, congressional Democrats unable to breach stalemate over coronavirus relief MORE (R-Calif.), secured the backing of Speaker Paul Ryan Paul Davis RyanAt indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates Peterson faces fight of his career in deep-red Minnesota district MORE (R-Wis.) to enforce a swath of subpoenas probing the Justice Department’s use of the so-called Steele dossier in the probe.

And on Friday, two Republican senators asked the Department of Justice to open a criminal investigation into the author of the dossier, Christopher Steele.

“After reviewing how Mr. Steele conducted himself in distributing information contained in the dossier and how many stop signs the DOJ ignored in its use of the dossier, I believe that a special counsel needs to review this matter,” said Sen. Lindsey Graham Lindsey Olin GrahamThe Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Senate Democrats' campaign arm announces seven-figure investment to boost Graham challenger Graham: Comey to testify about FBI's Russia probe, Mueller declined invitation MORE (R-S.C.), who issued the referral with Senate Judiciary Chairman Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans signal openness to working with Biden Senators offer disaster tax relief bill Trump spikes political football with return of Big Ten season MORE (R-Iowa).

Grassley’s Democratic counterpart on the Judiciary Committee, Sen. Dianne Feinstein Dianne Emiel FeinsteinSenators offer disaster tax relief bill Democrats back away from quick reversal of Trump tax cuts Congress must save the Postal Service from collapse — our economy depends on it MORE (Calif.), says she was not consulted on the referral.

The increased action by Republicans comes in a midterm election year where the party is worried about losing its House and Senate majorities, given President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE’s anemic poll numbers. While the Senate map gives the GOP good odds to continue its majority, members of both parties see potential for Democrats to retake the House.

The dossier has become a key weapon in Republican attempts to undermine the Mueller probe, as lawmakers have questioned whether the shadowy document was used as the justification for a politically-motivated investigation into whether the Trump campaign colluded with Moscow to swing the election.

Members of the conservative House Freedom Caucus have also questioned whether the dossier was used as the basis for an application for a surveillance warrant on Trump.

Some conservatives on Capitol Hill have targeted Mueller directly, arguing that he has stacked his team with lawyers who supported Trump’s campaign rival, Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE.

“We’ll investigate the unprecedented bias against President Trump that exists when we allow people who hate the president to participate in the investigations against him,” Rep. Matt Gaetz Matthew (Matt) GaetzLara Trump campaigns with far-right activist candidate Laura Loomer in Florida House to vote on removing cannabis from list of controlled substances The Hill's 12:30 Report: Sights and sounds from GOP convention night 1 MORE (R-Fla.) said in December.

But those attacks — on Mueller and on the Justice Department more broadly — have made some Republicans on Capitol Hill uncomfortable. Rep. Trey Gowdy Harold (Trey) Watson GowdySunday shows preview: Election integrity dominates as Nov. 3 nears Tim Scott invokes Breonna Taylor, George Floyd in Trump convention speech Sunday shows preview: Republicans gear up for national convention, USPS debate continues in Washington MORE (R-S.C.) told reporters recently that his “heart would be broken” if Nunes followed through with plans to investigate “corruption” at the FBI, for example.

“My colleagues on [the House Intelligence Committee] would tell you some days I can’t remember if I still work for the Department of Justice,” he said. “I am a defender of the Department of Justice more than I am an attacker.”

Leadership in both the House and Senate have said that Mueller should be allowed to finish his work unimpeded.

The dossier is a compendium of opposition research, including false claims and other information that has been confirmed, into then-candidate Trump, alleging multiple points of contact with Russia. It was paid for during the primaries by The Washington Free Beacon and later by the Democratic National Committee and the Clinton campaign.

The New York Times reported earlier this month that the FBI’s attention was initially drawn to the Trump campaign’s contacts with Russia not by the dossier, but by a representative of Australia’s government who had met with then-Trump campaign staffer George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE, who has since pleaded guilty to charges of making false statements to the FBI.

Critics of the dossier, however, have largely dismissed the account in the Times.

“Belief in this narrative requires one to blatantly disregard a series of fundamental questions,” like why did the FBI wait more than six months to interview Papadopoulos, wrote Reps. Mark Meadows Mark Randall MeadowsTrump won't attend UN General Assembly in person, Meadows says McConnell focuses on confirming judicial nominees with COVID-19 talks stalled Overnight Health Care: Ex-Pence aide backs Biden over virus response | Trump's sharp words put CDC director on hot seat | Trump coronavirus adviser threatens to sue Stanford researchers MORE (R-N.C.) and Jim Jordan James (Jim) Daniel JordanHouse passes resolution condemning anti-Asian discrimination relating to coronavirus Republicans call for Judiciary hearing into unrest in cities run by Democrats Trump, GOP seek to rebut Democratic narrative on night one MORE (R-Ohio) in a Thursday op-ed calling for Sessions to leave.

Despite the “manufactured hysteria” over the investigation, Meadows and Jordan wrote, “a simple truth remains: There is no evidence of any collusion between the Trump campaign and the Russians.”

Sessions has been unable to control what they described as a parade of leaks from the bureau, Meadows and Jordan wrote, and must step aside.

Mueller’s name is not mentioned in the op-ed.

If Sessions stepped down, it would open the door for Trump to appoint a replacement open to dismissing the special counsel. Because Sessions has recused himself from the Russia probe, the power to fire Mueller currently rests with Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE.

Trump has railed against Sessions for the recusal, which he reportedly believes was an abrogation of the attorney general’s duty to “protect” him.

Nunes has been one of the fiercest attack dogs in pursuit of the dossier. He has for months been involved in a feud with Justice Department over access to information related to how the bureau used the dossier, including whether or not it paid Steele. He has threatened to hold senior officials in contempt of Congress if they did not comply — a bid that was ultimately successful with Ryan’s backing this week.

It is common practice for the FBI to pay informants, one former senior FBI official who worked on national security issues told The Hill.

The former official also noted that, in general, the application for a surveillance warrant involves several layers of authentication of information, suggesting that if any of the information from the dossier were used in an application, it would have been corroborated. Justice Department lawyers often modify orders based on feedback from the court — and they must show probable cause that the target is acting as an agent of a foreign power.

Trump has said that he expects to be treated “fairly” by Mueller, although he has repeatedly derided the probe as a sham and a “witch hunt.” The investigation has so far produced two indictments, including Trump’s former campaign chairman Paul Manafort Paul John ManafortBannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention Ukraine language in GOP platform underscores Trump tensions MORE, and two guilty pleas, including onetime national security adviser Michael Flynn.

“For the purposes of hopefully thinking I'm going to be treated fairly, I've stayed uninvolved with this particular matter,” Trump told the Times.