Deputy Attorney General Rod Rosenstein says he consults with a career ethics official when questions arise about Attorney General Jeff Sessions' recusal from the Russian Federation investigation.
After President Donald Trump's friend, Newsmax CEO Chris Ruddy, said Monday night that Trump is considering firing Mueller, Rosenstein said Mueller can "only be fired for good cause", and it would be his job to put that good cause into writing.
But Stephen Gillers, a New York University professor who specializes in legal and judicial ethics, said the Mueller interview with Trump presented "no conflict whatsoever".
If Mueller knew he was going to be named special counsel, it is unlikely he divulged that information to Trump.
ROSENSTEIN: Well, no, because it's not necessary, because the department is a hierarchy, and so nothing gets to the attorney general about matters he's recused from unless they come through my office.
Asked whether he had seen any reason for Mueller to be removed, Rosenstein responded, "No, I have not".
He says he is confident that Mueller will have "the full independence he needs" to investigate thoroughly.
In an interview with ABC News on Sunday, Trump attorney Jay Sekulow said he didn't want to speculate on whether or not the president would fire Mueller.
White House spokeswoman Sarah Huckabee Sanders said: "Chris speaks for himself". "With respect to this subject, only the president or his attorneys are authorised to comment".
He also told the senators, "I can assure you we're going to do the right thing and defend the integrity of the investigation". "If there were not good cause, it wouldn't matter to me no matter what anybody says", explained Rosenstein.
Former House Speaker Newt Gingrich, an informal Trump adviser, tweeted Monday, "Republicans are delusional if they think the special counsel is going to be fair".
Schatz asked Rosenstein whether it was Sessions could possibly be a witness in the investigation, but Rosenstein refused to talk about it.
Trump supporters are mounting a campaign to have the US President fire Special Prosecutor Robert Mueller, who is tasked with investigating Russian subversion of the 2016 elections, amid expressions of adulation and sycophancy by his cabinet colleagues that has drawn derisive comparison to what happens in dictatorships and totalitarian regimes. Rosenstein said that while it depends on the circumstances, "I think the general answer is no".
The White House was quick to dismiss Ruddy's comments.
Trump has expressed frustrations with Sessions, one of the president's earliest high-profile backers.
Gingrich noted the congressional testimony last week of James Comey, whom Trump fired May 8 as director of the Federal Bureau of Investigation, who acknowledged that he had leaked his own memos of his conversations with Trump to force the appointment of an independent counsel. Short of impeachment, only the attorney general - in this case, Acting Attorney General Rod Rosenstein - can do so.
Mr Sessions vigorously denied having an undisclosed meeting with Russia's ambassador to the US.
Trump, however, lacks the legal authority to directly fire Mueller.
Rosenstein is scheduled to testify today before both Senate and House subcommittees regarding the Justice Department's budget, and he is likely to be questioned about Mueller's status.