WASHINGTON (Reuters) - Democrats in the U.S. House of Representatives rallied behind Special Counsel Robert Mueller on Thursday, after recent attempts by Republicans and conservative news outlets to discredit him and his probe into Russian interference in the 2016 presidential election.

In a letter sent to Justice Department Deputy Attorney General Rod Rosenstein, 171 of the 193 Democrats in the House said they support Mueller’s probe, and urged Rosenstein to let it continue “unfettered by political influence or threats to his authority.”

“We will not stand by and allow Fox News and right-wing Republicans to defy the rule of law and create their own rules to interfere with the legitimate investigation under the Constitution of the United States,” California Democrat Maxine Waters said during a press conference Thursday.

“There is an organized effort by Republicans ... to spin a false narrative and conjure up outrageous scenarios to accuse Special Counsel Mueller of being biased,” she added.

Rosenstein appointed Mueller as Special Counsel in May, after President Donald Trump fired former FBI Director James Comey for what Trump later said was “this Russia thing.” Critics promptly accused the president of trying to obstruct the probe.

Mueller is investigating whether Trump’s presidential campaign colluded with Russia to interfere with the election. Russia has denied meddling and Trump has said there was no collusion.

Republican criticism of Mueller, himself a member of their party, has intensified in recent months since he charged four of Trump’s close associates, including former campaign manager Paul Manafort and former National Security Adviser Michael Flynn.

Republicans and talk show hosts on Fox News have accused Mueller’s team and the Federal Bureau of Investigation of bias, citing issues including anti-Trump text messages exchanged between two FBI staffers who previously worked on Mueller’s team.

House Republicans have launched their own investigation into the FBI’s handling of Hillary Clinton’s emails, and questioned whether she received favorable treatment after no charges were brought.

Recently, rumors have flown around Washington that Trump may be seeking to have Mueller fired. Trump’s lawyers have said that is not true.

Rosenstein, also a Republican, oversees Mueller’s team. He can only fire Mueller for good cause, and he told Congress last week he sees no legitimate basis for doing so.

“This investigation must continue unimpeded,” House Judiciary Committee Ranking Democrat Jerrold Nadler said Thursday. Nadler said Republicans were trying to “provide cover for the President as the walls close in on him.”