The Wall Street Journal editorial page, the high priest of corporate conservatism, has emerged as one of the President Donald Trump’s staunchest allies in his efforts to undermine the investigation into whether his campaign colluded with Russia during the 2016 election.

On Monday, the Journal excoriated Special Counsel Robert Mueller and the FBI for withholding information from Congress about the firing of a top agent who reportedly sent anti-Trump messages.

Mueller reassigned a top FBI agent, Peter Strzok, over the summer after it was discovered that Strzok had sent anti-Trump text messages, The New York Times reported over the weekend. Strzok led the investigation into Hillary Clinton’s private email server and held a top role in the Russia probe, which Mueller has been leading since Trump fired former FBI director James Comey. Trump has repeatedly called the investigation a “witch hunt” and has acknowledged that he fired Comey at least partly due to the probe.

“Mr. Mueller and the Justice Department kept this information from House investigators, despite Intelligence Committee subpoenas that would have exposed those texts,” the Journal wrote in an editorial published Monday. “They also refused to answer questions about Mr. Strzok’s dismissal and refused to make him available for an interview.”

The Journal also takes issue with the fact that the woman who Strzok reportedly exchanged the text messages with, FBI lawyer Lisa Page, worked for Mueller and deputy FBI director Andrew McCabe.

“All of this reinforces our doubts about Mr. Mueller’s ability to conduct a fair and credible probe of the FBI’s considerable part in the Russia-Trump drama,” they wrote. “Mr. Mueller ran the bureau for 12 years and is fast friends with Mr. Comey, whose firing by Mr. Trump triggered his appointment as special counsel. The reluctance to cooperate with a congressional inquiry compounds doubts related to this clear conflict of interest.”

The editorial called upon Mueller to step down “in favor of someone more credible.”

It’s not the first time the Journal’s editorial board has called for Mueller’s ouster. In one October editorial, the board questioned Mueller’s credibility and called for an investigation into whether Democrats and the FBI colluded with Russia, rather than Trump.

“It is no slur against Mr. Mueller’s integrity to say that he lacks the critical distance to conduct a credible probe of the bureau he ran for a dozen years,” the editorial said. “He could best serve the country by resigning to prevent further political turmoil over that conflict of interest.”

In another piece, the board reacted to news that former Trump campaign manager Paul Manafort was being charged in connection with Mueller’s probe by saying that “the main charge against Donald Trump is poor judgment for hiring the notorious Beltway operator.”

In addition to the seething editorials, the newspaper has also published a series of opinion pieces from contributors attacking the Mueller probe, including one that accused the investigation of “imperil[ing] the rule of law.”

The Journal board’s conservative lean has been long-documented, but the election of Trump has reportedly created an internal newsroom struggle about how to cover the presidency, particularly as Mueller’s investigation has ramped up. Reports have surfaced that some staff are frustrated with Gerard Baker, the editor-in-chief, who is said to have pushed more commentary that’s defensive of the president.

Rupert Murdoch, who is known as a friend of Trump’s, owns the paper.