Democratic and Republican lawmakers on Sunday defended 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 and his investigation amid attempts by conservatives to discredit the probe.

Conservative pundits and some Republican lawmakers have questioned Mueller’s investigation after a report about the potential bias of an FBI agent previously assigned to the Russia probe.

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But Trump's defenders on Saturday took an additional step to cast doubt on Mueller’s investigation, with a lawyer for the president’s transition team telling congressional committees in a letter that Mueller’s investigation illegally obtained emails from the transition team. Mueller's office denied that the documents were obtained illegally.

Even as Mueller faces intensifying criticism from some quarters, both Republicans and Democrats during Sunday television interviews defended the integrity of the Russia investigation, which has consumed the Trump administration for the better part of its first year in the White House.

Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas), the No. 2 Republican in the Senate, defended Mueller, but insisted the special counsel must rid itself of any partisan investigators.

“I have a lot of admiration and respect for Director Mueller,” Cornyn told ABC’s “This Week."

“But I would think he would want to eliminate challenges to the integrity of his investigation by eliminating agents who have taken positions either in text messages or through their political activity that undermine the integrity of the results of the investigation.”

A former member of Mueller's team, FBI agent Peter Strzok, sent partisan messages to Lisa Page, another former member of the team, last year during the presidential campaign. Mueller reportedly removed the agent from his team after the messages were discovered. Cornyn praised the move.

Several other members of Mueller's team have donated to Democratic presidential campaigns and organizations in the past, according to Federal Election Commission filings.

Sen. James Lankford James Paul LankfordMcConnell works to lock down GOP votes for coronavirus bill Charities scramble to plug revenue holes during pandemic Warren calls for Postal Service board members to fire DeJoy or resign MORE (R-Okla.), who sits on the Senate Intelligence Committee and is therefore part of the panel’s own Russia investigation, said he does not think an agent on Mueller's team sending some anti-Trump messages “taints the entire process” of the special counsel’s probe.

“Obviously, I don't think it taints the entire process. But it certainly taints that season of it,” Lankford told CBS’s “Face the Nation.”

“And it's something you should look at with any political investigation that he was on at the time," Lankford continued. "Again, we want our FBI agents to be neutral and to be nonpolitical. Not very actively engaged politically.”

But Lankford emphasized that the special counsel must determine if the agent was “directing the investigation one way or the other.”

Democrats have long defended Mueller’s investigation and warned against any attempts to end the probe, with bipartisan groups of lawmakers introducing legislation aimed at protecting the special counsel.

Sen. Chris Van Hollen Christopher (Chris) Van HollenCongress must finish work on popular conservation bill before time runs out Democrats fear Russia interference could spoil bid to retake Senate Mid-Atlantic states sue EPA over Chesapeake Bay pollution MORE (D-Md.) defended Mueller on Sunday and called on Republicans to end their attacks on the investigation.

“You have got somebody who, by all accounts, is an independent person, somebody who has got lots of integrity,” Van Hollen told ABC’s “This Week.”

“And you see a concerted effort out of the White House to undermine the investigation. I really hope our Republican colleagues will not join in subverting that process and trying to end this investigation.”

Sen.-elect Doug Jones (D-Ala.), who as a Democrat from a deep-red state is likely to walk a fine line in the Senate between the two parties once he is sworn in, defended Mueller and said he doesn’t see any reason why the probe could be “tainted.”

“I would be very surprised if Bob Mueller did anything that illegally obtained or anything like that,” Jones told CNN's Jake Tapper on "State of the Union." “He is the consummate professional. And that investigation is proceeding. It's going to go forward. I don't see any taint at this point.”

Sen. Joe Manchin Joseph (Joe) ManchinManchin defends Supreme Court candidate Barrett: 'It's awful to bring in religion' The Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House MORE (D-W.Va.), a red-state Democrat who is on the Senate Intelligence Committee, said he does not think Mueller nor the investigation have been “compromised.”

“I think that he is the person, the right person, that when he finishes his investigation that we're going to have confidence it was done in a fair and balanced way. I truly believe that,” Manchin told NBC’s “Meet the Press.”

The White House, for its part, has denied rumored plans to fire Mueller, which a top administration aide reiterated during another Sunday interview.

“There's no conversation about that whatsoever in the White House, Chuck,” White House legislative affairs director Marc Short told NBC’s “Meet The Press."

“You guys keep bringing that up. We've continued to cooperate at every single possible way with that investigation," he said.

Mueller's team issued a rare statement defending its methods following the controversy over obtaining documents.

“When we have obtained emails in the course of our ongoing criminal investigation, we have secured either the account owner’s consent or appropriate criminal process,” special counsel spokesman Peter Carr said in a statement to The Hill on Sunday.

Mueller’s probe has led to the indictment of two former Trump campaign officials and a guilty plea from former national security adviser Michael Flynn.

Former Trump campaign chairman Paul Manafort Paul John ManafortOur Constitution is under attack by Attorney General William Barr Bannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention MORE and his former business associate, Richard Gates, pleaded not guilty to charges related to their political work in Ukraine.

Flynn, however, pleaded guilty to lying to the FBI about his conversations with the Russian ambassador to the United States. Former Trump campaign advisor George Papadopoulos has also pleaded guilty to lying to the FBI.